Toggling 'Drumset' twice in Mixer loses instrument and leaves some note heads as crosses

1. Take a score, any score should do, best a non-piano and non-drum score
2. Open the mixer
3. tick 'Drumset'
4. untick 'Drumset'

Expected result: everything is back to what it was before

Actual result:

• The instrument (sound has changed to "Yamaha Grand Piano"
• Some notes still have a cross head.

Came up in https://musescore.org/de/node/78991

MuseScire 2.0.2, Windows 7 (Enterprise, 64bit), as well as the latest development build, b376184