[Linux] Tooltip shown when I hover over the seek bar remains on the screen after I switch to another window

Hi I can reproduce the behavior mentioned in the summary with VLC 3.0.8 on linux systems running Gnome 3.34.1 or KDE Plasma 5.16.5 desktop environments.

open any app play a video with VLC player hover over the seek bar of VLC player while the tooltip showing the time is visible, switch to another app by pressing alt+tab Result: the tooltip of VLC player remains on the screen until you hover over it

Already reported in Gnome issues tracker. Olivier Fourdan developer said it seems a Qt/VLC bug. https://gitlab.gnome.org/GNOME/mutter/issues/856#note_624622

I'm reporting here because I can't reproduce the same behavior with SMPlayer, another Qt player that also shows a tooltip when we hover over its seek bar. I'm attaching a screen recording showing the issue with VLC.

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