I'm using Ubuntu 18.04 and this happens pretty much with every app.
When I'm using an app that has some sort of hover functionality, and when that hover functionality is triggered (ie a pop up appears) then when I switch to another app using the window switch (
tab) that pop up will remain:
For example, here's the remains of a sublime text 3 hover hanging around on Firefox:
Can I do anything to fix this? Is it a bug? Where should I report it if it is?