http://bugs.winehq.org/show_bug.cgi?id=4140
--- Comment #13 from Thomas Arendsen Hein thomas@intevation.de 2009-11-03 05:47:59 --- I filed a separate bug for the regression: http://bugs.winehq.org/show_bug.cgi?id=20565 (Emu42: regression in StretchBlt causes black display background)
Maybe this gives a hint about the problem, the commit talks about client-side optimizations. Maybe they optimize too much?