http://bugs.winehq.org/show_bug.cgi?id=24527
--- Comment #4 from Louis Lenders xerox_xerox2000@yahoo.co.uk 2010-09-27 11:23:44 CDT --- (In reply to comment #3)
Probably UpdateWindow() unlike RedrawWindow() should reject hwnd being 0. That would need a test case.
I wrote a tiny test and UpdateWindow returns indeed FALSE in case hwnd being. I'll send a patch + testcase.