http://bugs.winehq.org/show_bug.cgi?id=2181
--- Comment #34 from coldhands@ariel.hopto.org 2009-07-28 09:15:22 --- Yes, EDIT_builtin_class. It creates a "subclass" and reserves extra window memory for pointer storage. Most of the time it uses an index relative to the original cbWndExtra value when calling Get/SetWindowLong, but one spot in the window procedure is hardcoded. Definite brain damage.