https://bugs.winehq.org/show_bug.cgi?id=47165
--- Comment #34 from Hajo Krabbenhöft bugzilla+winehq.org@hajo.me --- I've finally figured out what caused the black UI :)
Between CreateDCRenderTarget, SetTarget, BindDC, etc. and then finally BeginDraw, iTunes was modifying the bitmap selected into the HDC by blitting into it. Wine will overwrite that "output bitmap" inside EndDraw/Present with the current state inside the "internal bitmap" that Wine creates inside BindDC. That's how the background got lost but the text remained.
The fix in my proposed patch is rather primitive: Inside BeginDraw, I copy data between the two bitmaps in exactly the other direction as what EndDraw/Present does. That way, any data that was present in the bitmap selected by the bound HDC before BeginDraw will also be retained in the final image, if it was not painted over. And that means iTunes' text drawing logic will no longer replace the background with a black square :)