http://bugs.winehq.org/show_bug.cgi?id=30256
--- Comment #4 from Matteo Bruni matteo.mystral@gmail.com 2012-03-26 12:58:39 CDT --- Created attachment 39556 --> http://bugs.winehq.org/attachment.cgi?id=39556 Update the right mask.
I attached a patch which should be correct and remove many unneeded glDrawBuffers() calls (which probably aren't free). However, the affected code was introduced AFTER the patch from the regression test, so I guess your issue is different... Anyway, I'd appreciate if you could test this patch, just in case.
Reading the log I had another idea though. Could you try the patch from bug 27879 and see if it helps here too?