Instrument change uses sound of original entry for all, except last

1. Open attached score (produced in 1.3).
2. 'View'>'Mixer'.
3. Apply instrument change in bar 2.
4. Change sound in Mixer (e.g. Piano).
5. Apply instrument change in bar 3.
6. Change sound in Mixer (e.g. Harpsichord).
7. Apply instrument change in bar 4.
8. Change sound in Mixer (e.g. Clavinet).
9. Play score from start.

Result: The sound in bar 2 and 3 uses that of the original entry (Synth Bass, instead of Harpsichord and Clavinet respectively).

Notes:

It also seems reproducible in a 2.0 score.
It is fine if you save, close and re-open - or open another score, then return.

Using MuseScore 2.0 Nightly Build 5020852 - Mac 10.7.5.