First it happened with the "Image Size..." dbox, which is available from the toolbar dropdown menu (Views|Customise) control on the Genres sub-node.
I closed MM5, and deleted my persistent.json file from \MediaMonkey 5\Portable ... then tried again ... it was OK
Then later a similar thing happened again ... here ... MM5 is maximised ... the screenshot is of my whole of the screen ... I tried to open the Track Properties dbox ... the dbox has opened off screen ... MM5 appears as if it has frozen, because it is waiting on the (mostly invisible) modal dbox.
- I clean installed a (portable) MM5, allowing it to import settings from MM4
- when it opened, it opened not maximised ... I maximised it
- I navigated to EntireLibrary>Genres, and pressed "Image Size..." ... the dbox opened at the left (not fully onscreen, as shown here)
- I pressed it's cancel button ... and opened it again ... this time it opened nearly off screen
- it continues to open off-screen until I drag it elsewhere
nb. I don't know whether it is relevant, but I have dual screens
I PM'd a copy of my persistent.json file to Ludek