Bug Animatiion window bugs

Clicking on the Property button:

• the contextual menu sometimes disappear but the place holder that contains it remains. Closing it from the Animation window icon in the task bar is apparently possible, but...

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• closing the Animation window using the cross icon on the top right doesn't make it disappear,

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• clicking outside the place holder makes it apparently disappear, but...

But...

Thinking that the thing had completely disappeared, I saved the layout as an external file and when I loaded it in the project, I got this (you see that the place holder has been recorded in the layout and Unity doesn't like that at all, neither do I for that matter:

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Happens in 2020.3 and 2021.1. I'm not sure how easy it would be to reproduce it though.

I'm on Linux Mint, details in my profile.