[Trunk] Clef issues with Delete selected measures on first bar of 1.0 score

Using MuseScore 1.0:

1. Create piano score.
2. Enter some notes.
3. Save.

Using MuseScore 2.0 Nightly Build (4387):

4. Open score.
5. Drag-select a note in the first bar.
6. Delete selected measures.
(Result: Everything is treble clefs.)
7. Undo.
(Result: The second bar onwards is all treble clefs, but the original clefs at the beginning have restored.)

Mac 10.6.7.