Open the Gimp (in my case in Spanish)
Use the Wacom's pen or mouse to move the pointer
A dos command window opens with this text:

----8<--cut-here--8<----8<--cut-here--8<----8<--cut-here--8<

(gimp-2.0.exe:2920): Gdk-WARNING **: losing last reference to undestroyed window



(gimp-2.0.exe:2920): GLib-GObject-CRITICAL **: file gobject.c: line 1320 (g_obje
ct_ref): assertion `object->ref_count > 0' failed

(gimp-2.0.exe:2920): GLib-GObject-CRITICAL **: file gobject.c: line 1338 (g_obje
ct_unref): assertion `object->ref_count > 0' failed

(gimp-2.0.exe:2920): GLib-GObject-CRITICAL **: file gobject.c: line 1338 (g_obje
ct_unref): assertion `object->ref_count > 0' failed

----8<--cut-here--8<----8<--cut-here--8<----8<--cut-here--8<

Application still works but you can't paint anymore even with a normal mouse. 
If you close the command window The Gimp closes too.

Using Windows XP SP1 with a Wacom Graphire2 with 4.78-6 drivers