Cannot use hyphen as keyboard shortcut for flat

From yingdat http://musescore.org/en/node/1512

"When I define a hyphen (-) as a shortcut for flat, it seems to work fine during that session of MuseScore. Once I exit and come back to MuseScore, that shortcut no longer works and indeed is no longer in the shortcut table. This seems to happen only with the - key and I see no conflict in the table."

r. 1723, Windows XP

The hyphen seems to work for other functions such as trill. It just doesn't work for flats.