Andy Piper <andy(a)xemacs.org&gt; writes: I was hitting the same bug. I now disabled that particular check and replaced it by static void check_frame_subwindow_instance_cache (struct frame* f) { Lisp_Object rest; LIST_LOOP (rest, XWEAK_LIST_LIST (FRAME_SUBWINDOW_CACHE (f))) { Lisp_Object value = XCAR (rest); ERROR_CHECK_IMAGE_INSTANCE (value); } } int inhibit_subwindow_check = 0; void check_subwindow_instance_caches (void) { Lisp_Object frmcons, devcons, concons; if (inhibit_subwindow_check) return; FRAME_LOOP_NO_BREAK (frmcons, devcons, concons) { check_frame_subwindow_instance_cache (XFRAME (XCAR (frmcons))); } } I then stuck this test in Feval, Ffuncall & at the end of Fset_window_configuration. If then start gnus, open up the xemacs-review list in Gnus 5.8.7, read a few message (some of them force gnus-picon to be loaded, although no picons are displayed) and q the Group I always get crashes in gnus-configure-windows. The deleted window in question is the Gnus *Article* buffer. Jan