Dear Maintainer,
I allowed the windows to cover my taskbar. When I move the mouse close to the
bottom, while a window is still covering it, the blue line appears. When
I move the mouse even more to the bottom, the taskbar shows up. When I then
switch the window sometimes this blue line does not disappear, even when
playing videos in VLC. It stays visible until I move the mouse again to the
bottom.
Several people reported this minor bug already before the actual stable
version, but nothing changed. Maybe upstream is still sleeping?