Description of problem:
1. Add new panel
2. Add "Window list" to the panel
3. Delete the panel

Version-Release number of selected component:
mate-panel-1.5.6-1.fc18

Additional info:
backtrace_rating: 4
cmdline:        mate-panel
crash_function: g_datalist_id_dup_data
executable:     /usr/bin/mate-panel
kernel:         3.8.7-201.fc18.x86_64
uid:            1000
ureports_counter: 1

Truncated backtrace:
Thread no. 1 (10 frames)
 #0 g_datalist_id_dup_data at gdataset.c:864
 #1 g_datalist_id_get_data at gdataset.c:798
 #2 g_object_get_qdata at gobject.c:3084
 #3 _gtk_widget_get_aux_info at gtkwidget.c:9364
 #4 gtk_widget_set_usize_internal at gtkwidget.c:7950
 #5 gtk_widget_set_size_request at gtkwidget.c:8057
 #6 tasklist_update at window-list.c:67
 #7 display_all_workspaces_changed at window-list.c:229
 #8 g_cclosure_marshal_VOID__STRINGv at gmarshal.c:1004
 #9 _g_closure_invoke_va at gclosure.c:840