The segfault occurs in a path in import.c that has a comment "XXX this
this should really not happen.":

Program received signal SIGSEGV, Segmentation fault.
0x000000000047d733 in type_dealloc (type=0x8381e0) at Objects/typeobject.c:2694
2694        _PyObject_GC_UNTRACK(type);
(gdb) bt
#0  0x000000000047d733 in type_dealloc (type=0x8381e0) at Objects/typeobject.c:2694
#1  0x000000000045d8ef in free_keys_object (keys=0x8eb810) at Objects/dictobject.c:374
#2  0x0000000000463513 in dict_dealloc (mp=0x8fa9c0) at Objects/dictobject.c:1392
#3  0x0000000000503118 in _PyImport_FixupExtensionObject (mod=0xa0cd40, name=0xb1fa90, 
    filename=0xb1fa90) at Python/import.c:498



(gdb) f 3
#3  0x0000000000503118 in _PyImport_FixupExtensionObject (mod=0xa0cd40, name=0xb1fa90, 
    filename=0xb1fa90) at Python/import.c:498
498                 Py_DECREF(def->m_base.m_copy);
(gdb) l
493         if (def->m_size == -1) {
494             if (def->m_base.m_copy) {
495                 /* Somebody already imported the module,
496                    likely under a different name.
497                    XXX this should really not happen. */
498                 Py_DECREF(def->m_base.m_copy);
499                 def->m_base.m_copy = NULL;
500             }
501             dict = PyModule_GetDict(mod);
502             if (dict == NULL)