http://bugzilla.openedhand.com/show_bug.cgi?id=1343
Index: matchbox-window-manager-1.2/src/select_client.c
===================================================================
--- matchbox-window-manager-1.2.orig/src/select_client.c
+++ matchbox-window-manager-1.2/src/select_client.c
@@ -49,6 +49,8 @@ select_client_new(Wm *w)
 
    if (width == 0 || height == 0) return NULL;
 
+   if (w->stack_top_app == NULL) return NULL;
+
    dbg("%s() got valid size\n", __func__);
 
    button_x = theme_frame_button_get_x_pos(w->mbtheme, FRAME_MAIN,