Musescore 2.2.1, black flashing when hovering a dropdown from menubar (layered windows?)

0.4.10-RC-30-g51a70dc gcc dbg lin
Musescore 2.2.1 from rapps (I think it's QT5 based)

Observed result
When you select an item in menubar and then hover with the mouse over the entries, the repaint draws that drop-down-menu with solid black for a fraction of a second, giving an ugly flickering effect.
0.4.10-RC-30-g51a70dc_vsMusescore2_2_1_blackflash.webm
Whenever it flickers, the following line is logged by ros:
0.4.10-RC-30-g51a70dc_blackflash.log

(../../win32ss/user/ntuser/layered.c:197) err: prcDirty

Is it related to our "problematic layered windows support"?

Expected result
I double-checked: Windows XP SP3 does not have this issue.
xpsp3_ok.webm