... or is this actually a garbage collection issue rather than compile  
pattern?

12  org.gnu.Emacs                 	0x000907ef fatal_error_signal + 319  
(emacs.c:385)
13  libSystem.B.dylib             	0x96a6a09b _sigtramp + 43
14  ???                           	0xffffffff 0 + 4294967295
15  libSystem.B.dylib             	0x96ae2ec2 raise + 26
16  libSystem.B.dylib             	0x96af247f abort + 73
17  org.gnu.Emacs                 	0x000ee385 mark_object + 181  
(alloc.c:5432)
18  org.gnu.Emacs                 	0x000ee92e mark_vectorlike + 94  
(alloc.c:5364)