Change drum instrument selection
Note entry for percussion staves requires selection of the drum instrument from the palette before placing the note. Changing a note afterwards with Up/Down cycles through the drum instruments in order of the palette.
For me as a drummer, this is unobvious. Even for complicated pieces I prepare a key where the instruments are distributed nicely over the note lines. It is much easier to change a misplaced note up or down a note line than following the palette definition.
There was a discussion in the forum some time ago with a good proposal (http://musescore.org/en/node/9762).