phred: the ghost lyrics that are "sticking" in the display panel are probably being pulled from the lyrics cache folder (MusicBee\AppData\InternalCache\Lyrics). Delete the cache contents regularly and you shouldn't see this. Of course you can do that manually but using a batch file makes it easier. Drop the following into an empty text file, rename as *.bat, and double-click when needed; check that the paths of my portable MB installation match yours:
@ECHO OFF
Set dir="c:\MusicBee\AppData\InternalCache\Lyrics"
Echo Deleting all files from %dir%
del %dir%\* /F /Q
Echo Deleting all folders from %dir%
for /d %%p in (%dir%\*) Do rd /Q /S "%%p"
@echo Folder deleted.
exit