Observed on Gentoo Linux by the submitter and now on Redhat as well: https://sourceforge.net/forum/forum.php?thread_id=2086437&forum_id=362510
iges-g run with the -n option on an iges file (the submitter used the openmoko IGES file as a test: http://downloads.openmoko.org/CAD/Neo1973_IGES_STEP.zip\)
iges-g -n -o phone.g gtc01-mme01_asm.igs
The above forum posting shows a backtrace which appears to duplicate the function calling sequence and ultimate failure point on Gentoo, although the original failure on Gentoo was simply a segmentation fault and the backtrace had to be done step-by-step.
When the above example was tested on MacOSX, the conversion completed without the free() related crash, so it may be OS specific.