OK, I narrowed it down to the exact keystrokes I need to cause the crash, attached gdb at the last minute, and crashed it. Program received signal SIGSEGV, Segmentation fault. 0x81e8a8e in ChangeManaged (wid=0x88a3800) at /ext/src/xemacs-21.0-b36/src/EmacsShell-sub.c:369 369 (((ShellWidgetClass) SUPERCLASS_WIDGET_CLASS)-> (gdb) bt #0 0x81e8a8e in ChangeManaged (wid=0x88a3800) at /ext/src/xemacs-21.0-b36/src/EmacsShell-sub.c:369 #1 0x400dc77c in x_focus_timestamp_really_sucks_fix_me_better () #2 0x400dcb7e in x_focus_timestamp_really_sucks_fix_me_better ()