TeamViewer 14 on Ubuntu 18.04 - Window always in foreground

Just installed TV14 on Ubuntu 18.04. I noticed that the content of the TeamViewer (TV) window is always in foreground, above any other windows. (The window which states your ID and random password and lets you connect to other clients.) 

If I have an other window overlap with the TV window, the TV window's titlebar (the top part in "ubuntu-look") gets covered, but the inner part of the TV window is drawn in foreground, hiding the other, active, window. It appears that I can "click through" the TV window (e.g. the other window has a button, i drag it behind the TV window, then guess where the button is, and click it)

If I move or minimize the TV window, it does nothing unusal.

Within the TV window, I can click on the lefthand icons ("connections" and "meetings") and they work. But anything that should be drawn above, does not work: Dropdown-Menus like "Connections" and "Help" do not work - at least, they do not appear to work - I suspect them to be drawn below the "eternal foreground" part of the window. Interesting: The "Connect" button in the top right corner offers a small dropdown menu, which is broad enough that part of it extend sideways, past the main window. When expanding this dropdown, I can see the part, which is not covered by the foreground TV window.

I just tried to start the ubuntu updater to get some latest packages. Usually, you click on "apply", then the screen darkens and you get prompted for your admin-password. The TV window stayed non-grayed-out on top of the darkening-effect and on top of the password prompt...