Click on newly created part tab crash (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. Click the X on the Alto tab to close the tab without ever switching window focus
7. Close the current Soprano tab

--> Crash

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

(Operating System: Windows 7)