https://bugs.winehq.org/show_bug.cgi?id=42585
--- Comment #7 from Rafał Mużyło galtgendo@o2.pl --- So, years later...
Anyway, with bug 30506 fixed by 3c8784bf9c1a897de021587437c5ec4f648c84a1, the (seemingly correct) fix for this problem seems to be adding 'if (!(src_color & 0xff000000)) src_color = 0;' condition to the '(comp_mode == CompositingModeSourceCopy)' branch.
Bug 30506 seem to confirm it for transparent black, this one for transparent white, so it's likely it's simply for transparent case.