[Trunk] Any change to drums causes notes to move down

1. Open score with drums.
2. Drag something (e.g. arpeggio) from the palette to a note in the drums stave.

Result: All notes in the drum stave move down.

Discussion: Undo does remove the object, but the notes do not return to their former position. Marking as critical as undo does not restore the former state.

Using MuseScore 2.0 Nightly Build (4814) - Mac 10.6.8.