Hello I might have found a bug.<div>I really cannot explain the following (please be indulgent as I narrowed the most I could).</div><div><br></div><div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">library(data.table)</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">DT = data.table(X=as.POSIXct( c(rep("15DEC2008:00:00:00",10)</span><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">,"15DEC2008:00:00:00",rep("</span><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">17DEC2008:00:00:00",2)),</span><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">format="%d%b%Y:%H:%M:%S"),Y=c(</span><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">1534,61,74,518,519,1519,1520,</span><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">1524,3127,29250,30609,43,7853)</span><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">)</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">setkey(DT,X,Y)</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"><br></span></div><div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">#Here is what I see after the sort </span></div>

<div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"><br></span></div><div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">DT</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">             X     Y</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 1: 2008-12-15  </span><span style="font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"><font color="#ff0000"><b>1534</b></font></span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 2: 2008-12-15    61</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 3: 2008-12-15    74</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 4: 2008-12-15   518</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 5: 2008-12-15   519</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 6: 2008-12-15  1519</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 7: 2008-12-15  1520</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 8: 2008-12-15  1524</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 9: 2008-12-15  3127</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">10: 2008-12-15 29250</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">11: 2008-12-15 30609</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">12: 2008-12-17    43</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">13: 2008-12-17  7853</span></div><div><br></div><div>#I thought that it was a POSIXct problem but if I can get the correct answer like this:</div>

<div><br></div><div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">DT[order(X,Y),]</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">             X     Y</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 1: 2008-12-15    61</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 2: 2008-12-15    62</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 3: 2008-12-15    74</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 4: 2008-12-15   518</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 5: 2008-12-15   519</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 6: 2008-12-15  1519</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 7: 2008-12-15  1520</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 8: 2008-12-15  1524</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> 9: 2008-12-15  3127</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">10: 2008-12-15 29250</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">11: 2008-12-15 30609</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">12: 2008-12-17    43</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">13: 2008-12-17  7853</span></div><div><br></div><div>#Here is my session (just launched it)<br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"><br></span></div><div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">R> sessionInfo()</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">R version 2.15.2 (2012-10-26)</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">Platform: x86_64-pc-linux-gnu (64-bit)</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">locale:</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> [1] LC_CTYPE=en_GB.UTF-8       LC_NUMERIC=C               LC_TIME=C                 </span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> [4] LC_COLLATE=en_GB.UTF-8     LC_MONETARY=fr_FR.UTF-8    LC_MESSAGES=en_GB.UTF-8   </span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"> [7] LC_PAPER=C                 LC_NAME=C                  LC_ADDRESS=C              </span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">[10] LC_TELEPHONE=C             LC_MEASUREMENT=fr_FR.UTF-8 LC_IDENTIFICATION=C       </span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">attached base packages:</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">[1] stats     graphics  grDevices datasets  utils     methods   base     </span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">other attached packages:</span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">[1] data.table_1.8.7 inline_0.3.10    Rcpp_0.10.2      vimcom_0.9-5     setwidth_1.0-2  </span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">[6] colorout_0.9-9  </span><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)">

<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13.333333969116211px;background-color:rgb(255,255,255)"><br></span></div><div><br></div>