http://bugs.winehq.org/show_bug.cgi?id=22369
--- Comment #16 from a.m.winehq@gmail.com 2010-04-19 05:41:57 --- I've attached a simple test project.
Build it, run it on Wine, open a few MDI child windows, select menu [Window]->[Tile], and you will see the bug. (blank in the client area)