Part appears empty (0.9.6 regression)

Steps to reproduce bug
1. Open "Choir score.mscz"
2. File > Parts
3. Create Parts for Soprano, Alto, and Piano (in that order)
4. Press "Close" to leave the parts dialog
5. Click on the newly created Soprano tab
6. Close the Soprano tab
7. Close the Alto tab

Expected behavior: After closing the Soprano tab in step 6 you should be able to see the Alto score. After closing the Alto tab in step 7 you should be able to see the Piano score

Actual behavior: The score area for the Alto and Piano tabs appear gray

MuseScore version: r. 2883. Bug not present in 0.9.5 stable

(Operating System: Windows 7)