When switching themes around a lot I often experience crashes in random apps,
including nautilus, gnome-panel, gnome-settings-daemon etc.

I've been running the theme manager under valgrind today and found the same
backtrace there with a warning about an "invalid read of size 1". This happened
while running the theme thumbnailer I think. Backtrace:

==756== Invalid read of size 1
==756==    at 0x1B90553A: strcmp (mac_replace_strmem.c:249)
==756==    by 0x1C25CE5D: IA__g_str_equal (gstring.c:69)
==756==    by 0x1C239C3E: IA__g_hash_table_lookup (ghash.c:203)
==756==    by 0x1C23584D: IA__g_quark_from_static_string (gdataset.c:592)
==756==    by 0x1CC5C1B6: smooth_rc_style_parse (smooth_gtk2_engine.c:75)
==756==    by 0x1BC4E639: gtk_rc_parse_style (gtkrc.c:3204)
==756==    by 0x1BC4EC85: gtk_rc_parse_any (gtkrc.c:2424)
==756==    by 0x1BC4F36B: gtk_rc_context_parse_one_file (gtkrc.c:827)
==756==    by 0x1BC4F451: gtk_rc_context_parse_file (gtkrc.c:893)
==756==    by 0x1BC4F635: gtk_rc_parse_named (gtkrc.c:644)
==756==    by 0x1BC4FA08: IA__gtk_rc_reparse_all_for_settings (gtkrc.c:1525)
==756==    by 0x1BC4FA68: gtk_rc_settings_changed (gtkrc.c:540)
==756==    by 0x1C201658: IA__g_cclosure_marshal_VOID__PARAM (gmarshal.c:531)
==756==    by 0x1C1ECD28: IA__g_closure_invoke (gclosure.c:437)
==756==    by 0x1C1FF949: signal_emit_unlocked_R (gsignal.c:2485)
==756==    by 0x1C2008CF: IA__g_signal_emit_valist (gsignal.c:2244)
==756==    by 0x1C200B1B: IA__g_signal_emit (gsignal.c:2288)
==756==    by 0x1C1EE7BA: g_object_dispatch_properties_changed (gobject.c:593)
==756==    by 0x1C1EDCC4: g_object_notify_dispatcher (gobject.c:234)
==756==    by 0x1C1F0B60: IA__g_object_set_valist (gobjectnotifyqueue.c:123)
==756==    by 0x1C1F0ED5: IA__g_object_set (gobject.c:1211)
==756==    by 0x805606A: message_from_capplet (theme-thumbnail.c:126)
==756==    by 0x1C268A8E: g_io_unix_dispatch (giounix.c:162)
==756==    by 0x1C245D70: IA__g_main_context_dispatch (gmain.c:1947)
==756==    by 0x1C24764E: g_main_context_iterate (gmain.c:2578)
==756==    by 0x1C2478CF: IA__g_main_loop_run (gmain.c:2782)
==756==    by 0x1BC19EB6: IA__gtk_main (gtkmain.c:963)
==756==    by 0x805717D: theme_thumbnail_factory_init (theme-thumbnail.c:609)
==756==    by 0x8050AA7: main (gnome-theme-manager.c:1441)
==756==  Address 0x1C63ACC8 is not stack'd, malloc'd or (recently) free'd

Marking this up and setting it on the 2.10.0 milestone since it's an important
fix for possibly a lot of crashes.