Zombie floating mode project / run / structure windows

I run IntelliJ with several windows such as Project, Run, Debug, Structure, Maven, Version Control all floating.

This is great for my layout since I've got two big screens, one of which I stand portrait mode - although I doubt that has anything to do with it.

Problem: when I change projects and open the new project in the same window, then IntelliJ loses track of the floating windows, they go dead and sit there uselessly like zombies until I close IntelliJ completely.

Here's a screenshot. The project window behind and the version control window below are zombies from the previous project which I just closed by opening the new one you see in the main window.

This  is on Windows 10 with the latest IntelliJ enterprise version.