Display-corruption on 'scroll music sheet' followed by 'move window'

Operating system: Mac OS X Yosemite (10.10)
MuseScore versions confirmed: 1efc609 (2.0 Beta 1) and 9686be7 (Nightly build 30/10/2014)

Steps to reproduce:
1 Open MuseScore
2 Use 2-finger swipe on trackpad with cursor above default music sheet to move the sheet around (scroll-gesture)
3 Use trackpad click&drag to move the window around
4 randomly repeat 2 & 3

Expected result: UI remains clean, either sheet music (2) or window (3) gets moved around on screen
Observed result: Sheet music (2) or window (3) gets moved around, but on (3) the non-sheetmusic UI parts get littered with partial sheet music engravings

Attached screenshots were made from 2.0 beta 1, behavior is the same with latest nightly. First screenshot is before moving window around, second is after a little move, third after a couple of random repetitions of steps (2) and (3) to show that screen corruption gets worse and worse