This is the crash:

(seahorse:10950): GLib-GObject-WARNING **: instance with invalid (NULL) class pointer

(seahorse:10950): GLib-GObject-CRITICAL **: g_signal_handlers_destroy: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed
==10950== Invalid read of size 8
==10950==    at 0x3939214857: g_object_unref (gobject.c:3017)
==10950==    by 0x4EF6E2: seahorse_certificate_dispose (seahorse-certificate.c:142)
==10950==    by 0x3939214787: g_object_unref (gobject.c:2986)
==10950==    by 0x3938A37272: g_hash_table_remove_all_nodes (ghash.c:536)
==10950==    by 0x3938A380F0: g_hash_table_remove_all (ghash.c:1345)
==10950==    by 0x3938A3815D: g_hash_table_destroy (ghash.c:1049)
==10950==    by 0x4EC439: seahorse_token_finalize (seahorse-token.c:672)
==10950==    by 0x393921486A: g_object_unref (gobject.c:3023)
==10950==    by 0x3938A44ACC: g_list_foreach (glist.c:942)
==10950==    by 0x3938A44AEA: g_list_free_full (glist.c:183)
==10950==    by 0x4E5113: seahorse_pkcs11_backend_dispose (seahorse-pkcs11-backend.c:202)
==10950==    by 0x3939214787: g_object_unref (gobject.c:2986)
==10950==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==10950== 
==10950== 
==10950== Process terminating with default action of signal 11 (SIGSEGV)
==10950==  Access not within mapped region at address 0x0
==10950==    at 0x3939214857: g_object_unref (gobject.c:3017)
==10950==    by 0x4EF6E2: seahorse_certificate_dispose (seahorse-certificate.c:142)
==10950==    by 0x3939214787: g_object_unref (gobject.c:2986)
==10950==    by 0x3938A37272: g_hash_table_remove_all_nodes (ghash.c:536)
==10950==    by 0x3938A380F0: g_hash_table_remove_all (ghash.c:1345)
==10950==    by 0x3938A3815D: g_hash_table_destroy (ghash.c:1049)
==10950==    by 0x4EC439: seahorse_token_finalize (seahorse-token.c:672)
==10950==    by 0x393921486A: g_object_unref (gobject.c:3023)
==10950==    by 0x3938A44ACC: g_list_foreach (glist.c:942)
==10950==    by 0x3938A44AEA: g_list_free_full (glist.c:183)
==10950==    by 0x4E5113: seahorse_pkcs11_backend_dispose (seahorse-pkcs11-backend.c:202)
==10950==    by 0x3939214787: g_object_unref (gobject.c:2986)
==10950==  If you believe this happened as a result of a stack
==10950==  overflow in your program's main thread (unlikely but
==10950==  possible), you can try to increase the size of the
==10950==  main thread stack using the --main-stacksize= flag.
==10950==  The main thread stack size used in this run was 8388608.
==10950== 
==10950== HEAP SUMMARY:
==10950==     in use at exit: 5,293,087 bytes in 41,149 blocks
==10950==   total heap usage: 384,346 allocs, 343,178 frees, 31,871,245 bytes allocated
==10950== 
==10950== LEAK SUMMARY:
==10950==    definitely lost: 19,757 bytes in 105 blocks
==10950==    indirectly lost: 12,608 bytes in 392 blocks
==10950==      possibly lost: 3,299,267 bytes in 25,546 blocks
==10950==    still reachable: 1,961,647 bytes in 15,110 blocks
==10950==         suppressed: 0 bytes in 0 blocks
==10950== Rerun with --leak-check=full to see details of leaked memory
==10950== 
==10950== For counts of detected and suppressed errors, rerun with: -v
==10950== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 3 from 3)
Killed