The extended black screen seems to be caused by the refresh rate issue (where the refresh rate is lowered when multi-tasking back into the game client). Essentially, the desktop refresh rate is different from the game client refresh rate when this issue triggers, similar to when game resolution is different to the desktop native resolution, which also causes an extended black screen.
We’re currently investigating a solution for both issues and planning to fix it for a future patch. I can’t give a timeline just yet, but they are priority issues.