I have recently upgraded from 2.4.x to 3.2.2 on Windows 10, and have noticed a very peculiar bug. When I have two project windows open, trying to adjust the volume or pan sliders in the second project causes Audacity to bring the other open project window to the foreground, making it impossible to adjust volume or pan on any track in the second project. The only way I have found to avoid this is to minimise the non-active project window before editing the active project, which is a rather clumsy workaround.
What seems to be happening here is that just hovering your cursor over the meter toolbars in the inactive (second) project window brings that project window to the top - but leaves the original project active active.
I think that this is a bug (Possibly a regression bug - I need to do some more testing). I will log this issue later.
Good catch mj10008 - and thanks for the report 
Peter
Testing shows that this is a regression on2.1.2 created long ago version 2,1,3.
I will be logging this later today,
Update
Now logged:
Hovering over the meters of an unfocussed project window brings that window to the front - original project retains focus #4094
https://github.com/audacity/audacity/issues/4094
Peter.
Thanks Peter. I think an important aspect to this bug is that the inactive window is brought to the front even if it was originally not visible on screen at all, e.g. because the active project window was maximised. It is this point that interferes with editing the active project. If both windows are maximised, the slider controls are in the same screen location on both projects and moving the pointer to that location brings the inactive window to the front.