Unticking drumset doesn't restore normal notes
1. Open piano score.
2. Open 'Mixer'.
3. Tick 'drumset'.
4. Change sound to 'Orchestra'.
5. Untick 'drumset'.
Expected result: The instrument list, notes and sound are restored.
Actual result: The instrument list is restored, but not the notes or sound.
Discussion: Marked critical, as it can ruin scores - undo doesn't work.
Using MuseScore 1.1 and 2.0 Nightly Build (4647) - Mac 10.6.8.