I found that when I close Google Chrome (42.0.2311.152 64-bit) on Ubuntu (14.10, 15.04) using Mod-Escape, goomwwm crashes and leaves me back at the login screen. I swapped my install for a debug build and found the following in my syslog:
May 17 00:03:53 gridge kernel: [ 2347.844741] goomwwm: segfault at 8 ip 0000000000403969 sp 00007ffc6fc28b18 error 4 in goomwwm[400000+19000]
I used addr2line to lead me to box.c:67 (box_hide), and found the offending caller to be client_close. I've added a guard around the box_hide call (like in client_review_border). The segfault no-longer happens.
Guard box_hide call on client_close