https://bugs.winehq.org/show_bug.cgi?id=56118
--- Comment #4 from Rafał Mużyło galtgendo@o2.pl --- Well, yes, but also no.
That is SHAppBarMessage is unlikely to matter here.
It seems to be some redraw order problem. Clicking in that black area sometimes makes the content of that subwindow to be shown, but not permanently so.