Sorry, not fixed! There's that similar dll plugin for iTunes (mmKeys) that solves the problem. I wonder what the magic is?
Or, a really easy fix would be to allow commands in the shortcut path of MusicBee. For example, -playpause, -nexttrack, -previoustrack, etc which then could be set as shortcuts for the keys on the keyboard.
This may be a sidenote, but the Beta start-up time is much faster!