I've recompiled gtk+, glib and whole xfce with debug flag on. It happens everytime I want to set options to any launcher icon.

desowin@localhost ~ $ gdb /usr/bin/xfce4-panel
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This GDB was configured as "i686-pc-linux-gnu"...(no debugging symbols found)
Using host libthread_db library "/lib/tls/libthread_db.so.1".
 
(gdb) run
Starting program: /usr/bin/xfce4-panel
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(xfce4-panel:10546): Gtk-CRITICAL **: gtk_accel_label_new: assertion `string != NULL' failed
 
(xfce4-panel:10546): Gtk-CRITICAL **: gtk_misc_set_alignment: assertion `GTK_IS_MISC (misc)' failed
 
(xfce4-panel:10546): Gtk-CRITICAL **: gtk_container_add: assertion `GTK_IS_WIDGET (widget)' failed
 
(xfce4-panel:10546): Gtk-CRITICAL **: gtk_accel_label_set_accel_widget: assertion `GTK_IS_ACCEL_LABEL (accel_label)' failed
 
Program received signal SIGSEGV, Segmentation fault.
0xb7dbd682 in gtk_widget_show () from /usr/lib/libgtk-x11-2.0.so.0
(gdb) bt
#0  0xb7dbd682 in gtk_widget_show () from /usr/lib/libgtk-x11-2.0.so.0
#1  0xb7cdbffc in gtk_image_menu_item_new_with_label ()
   from /usr/lib/libgtk-x11-2.0.so.0
#2  0xb762601f in launcher_save ()
   from /usr/lib/xfce4/panel-plugins/liblauncher.so
#3  0xb762789e in launcher_properties_dialog ()
   from /usr/lib/xfce4/panel-plugins/liblauncher.so
#4  0xb7623808 in xfce_panel_plugin_get_construct ()
   from /usr/lib/xfce4/panel-plugins/liblauncher.so
#5  0xb78dcd3d in g_cclosure_marshal_VOID__VOID ()
   from /usr/lib/libgobject-2.0.so.0
#6  0xb78cb2ac in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#7  0xb78db905 in g_signal_has_handler_pending ()
   from /usr/lib/libgobject-2.0.so.0
#8  0xb78dc54b in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#9  0xb78dc882 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#10 0xb7eed142 in xfce_panel_plugin_signal_configure ()
   from /usr/lib/libxfce4panel.so.1
#11 0xb78dcd3d in g_cclosure_marshal_VOID__VOID ()
   from /usr/lib/libgobject-2.0.so.0
#12 0xb78cb2ac in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#13 0xb78db905 in g_signal_has_handler_pending ()
   from /usr/lib/libgobject-2.0.so.0
---Type <return> to continue, or q <return> to quit---
#14 0xb78dc54b in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#15 0xb78dc882 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#16 0xb7db7883 in gtk_widget_activate () from /usr/lib/libgtk-x11-2.0.so.0
#17 0xb7d02d93 in gtk_menu_shell_activate_item ()
   from /usr/lib/libgtk-x11-2.0.so.0
#18 0xb7d02ee5 in gtk_menu_shell_activate_item ()
   from /usr/lib/libgtk-x11-2.0.so.0
#19 0xb7cf9c5a in gtk_menu_reorder_child () from /usr/lib/libgtk-x11-2.0.so.0
#20 0xb7cf4e00 in gtk_marshal_VOID__UINT_STRING ()
   from /usr/lib/libgtk-x11-2.0.so.0
#21 0xb78cb4de in g_cclosure_new_swap () from /usr/lib/libgobject-2.0.so.0
#22 0xb78cb2ac in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#23 0xb78dbaa0 in g_signal_has_handler_pending ()
   from /usr/lib/libgobject-2.0.so.0
#24 0xb78dc5ab in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#25 0xb78dc882 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#26 0xb7db7aea in gtk_widget_activate () from /usr/lib/libgtk-x11-2.0.so.0
#27 0xb7cf2a52 in gtk_propagate_event () from /usr/lib/libgtk-x11-2.0.so.0
#28 0xb7cf3aa5 in gtk_main_do_event () from /usr/lib/libgtk-x11-2.0.so.0
#29 0xb7baf0e9 in gdk_event_get_graphics_expose ()
   from /usr/lib/libgdk-x11-2.0.so.0
#30 0xb786812e in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#31 0xb78694b6 in g_main_context_acquire () from /usr/lib/libglib-2.0.so.0
---Type <return> to continue, or q <return> to quit---
#32 0xb786970f in g_main_loop_run () from /usr/lib/libglib-2.0.so.0
#33 0xb7cf30a2 in gtk_main () from /usr/lib/libgtk-x11-2.0.so.0
#34 0x0804fca5 in panel_app_run ()
#35 0x0804f5d3 in main ()
(gdb)