This only just started happening. When I move Full Screen MB from main right-hand monitor to secondary left-hand monitor, MB resizes Album Art and Visualiser panels (Left main panel). Could be just one of these two panels as one would affect the other. MB also resizes the right sidebar. The exact same thing happens if I Restore Down MB window in either monitor and re-maximise it. I have included two screen shots. "MusicBee-8" Is the right hand main display and you will see that the album covers number eight across, widthways. This screenshot is my preferred setup. "MusicBee-9" shows what happens when I shift the window to the left hand monitor or restore-down then re-maximise the window in either monitor. MB visibly shrinks the width of both side panels and you will see that the album covers display is now 9 albums wide. Moving the window back to the main display from secondary display does not return it to its previous layout, remaining as you see in MusicBee-9. As I move the window around a lot, depending on what I'm doing, this is becoming a real nuisance.
Windows 10 Home (fully up to date).
MB 3.5.8447 (latest build).
Both monitors are identical in brand, resolution and setup.
Behaviour happens every time the MB window is moved between screens or restored down and re-maximised.
Closing and re-starting will display the same layout as from which window it was closed.
MusicBee-8
MusicBee-9