[Trunk] Undo after Delete Selected Measures doesn't reinstate them until page is reset

1. Open score .
2. Drag-select a system.
3. 'Delete Selected Measures'.
4. Undo.

Expected result: Deleted measures are restored.
Actual result: Deleted measures aren't restored until you 'Reset'.

Using MuseScore 2.0 Nightly Build (4958) - Mac 10.6.8.