2 Launch MM for this user
3 Dismiss three dialogs
4 Drag Now Playing to float
5 Click Now Playing Dock to Window
Expected: Now Playing docks
Observed: Now Playing enters a weird state:

in which it
a) is often semi-transparent
b) cannot be dragged to dock
c) on title-bar right click shows a window control menu

rather than the usual NP options menu
d) responds to Dock to Window not by docking but by returning to normal state (#4)
3) cannot [EDIT:] easily be escaped if Now Playing Controls get hidden. Workaround: exit MM, in MediaMonkey.ini change NowPlayingDockable=0 to NowPlayingDockable=1 and relaunch.
Note: this may be a mutated form of the miniplayer NP window.
This on Win XP SP2, MM skinned and non.
EDIT(TC) Tracked at http://www.ventismedia.com/mantis/view.php?id=6826