Thanks for the bug report.  I can't reproduce the problem on my Fedora 
20 x86-64 desktop, but in reviewing xgselect.c I see some glitches that 
could explain things.  Please try the attached patch and let us know 
whether it helps with your problem.  Please compile with 
-DENABLE_CHECKING so that the patch's 'eassert' calls have teeth.  Thanks.