You are propably in a multi-screen environment. The in question top panel is probably between your two monitors. Panels and docks that are between screens they lose that characteristic under x11 and kwin combination. KWin can not handle the case under x11 and for that reason it is blocked.
If you use plasma panels you will get same results. Plasma has also blocked that characteristic under x11.
Are you or are you not using a multi-screen environment?
Yes, my primary screen is on the left bottom orientated in landscape, My secondary screen is above my primary screen. My third screen is in portrait mode on the right hand side of the 2 other screens.
Isnt your top panel between two of your monitors?
Yes it is located between my primary and second screen.
Plasma failing to identify the scenario is not Latte fault
Plasma panels acts as normal and are always visible. When a windows is maximized it does not
cover the window. As for latte it does.
If you report the case to Plasma they will also consider it a bug of Plasma
I don't think plasma will consider this as a bug because my widgets on the desktop move down when I move the latte panel from the bottom to the top of my screen.
Working? Really? Can you place any window at the screen above your top panel?
For the latte panel it is not working. But it is for a plasma panel. Any window that I maximize maximizes full screen. Acting as that the panel isn't there. And thus they go under the panel. So for example my browser tabs are not visible because they are hidden underneath the panel.
Since I cannot upload any pictures as a new user I will upload one to Imgur.