This is a very minor thing but I'm seeing it consistently. I have two monitors, one of which is 1920 x 1080 scaled to 125% and the other is 1280 x 1024 not scaled. Whenever I open a pop-up window that shows up in the same monitor as MusicBee, it applies the same scaling settings. However, if I have pop-up that opens in the other monitor, it uses the scaling setting of the monitor with the main MusicBee window UNTIL I move the pop-up a little bit (not back to the other window, even if I move it one pixel it snaps into the correct size). Interacting with the pop-up in other ways has no effect on the size.
To sum up:
MusicBee in 1024 monitor, pop-up in 1080 monitor = tiny pop up until I move it
MusicBee in 1080 monitor, pop-up in 1024 monitor = giant pop up until I move it