Hi all! Hi Jeff! Thank you all for this post, the solution and the discussion. Yet...

I've heard or read no one complain about Opera. The Browser. Yet, that's the one I use, and the issue is exactly the same. I reckon I can wait till my face grows a 3ft beard till that be fixed, right? What do you reckon?

Kindest regards from the Netherlands

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Part 2:
After having dealt with this for weeks (I mean, it's not the end of the world) I've found an ugly but easy quick fix, for anyone who still experiences this:

when your mouse is hovering over the WP admin menu, try zooming in (CTRL-+) and zooming back to normal (CTRL-0) again. That appears to set it all back into place for that moment.

Yes. A workaround. Ugly. Stupid even. But it works :)