If windows are displayed "always on top", they not only overlay all other windows, but also the popup application menu. This is of course pretty hindering and probably unwanted.
Where did you see the bug?
(In reply to Fushan Wen from comment #1) > Where did you see the bug? I just had a window maximized vertically but split horizintally (doesnt matter actually) and pinned to the front. Pressed the meta key
Can reproduce on Wayland.
Fixed in Plasma6