Tempo text oddities in score with linked parts until save/reopen

First reported at https://musescore.org/en/node/78251. I don't really know what's going on, but it's easy to reproduce similar issues with a new score. Here's exactly what I did:

1) Create new score from string orchestra template
2) In Volin I staff, quickly enter a mess of random notes
3) File -> Parts… -> New All
4) In main score, [Option]+[T] at measure one to create "Quarter = 80"
5) "Quarter = 120" at measure 3
6) "Quarter = 144" at measure 5
7) Double-click tempo at measure 3 and change to "Quarter = 60"

Everything will play back correctly in the main score. Now: switch to part for Violin I, and:

1) In the Inspector, though all tempos are set to "Follow Text", the first two (80 and 60) display "120" in the grayed out BPM box, and the third one (144) displays 80;
2) Actual playback tempo (as reported by the Play Panel) is 80 BPM at the first tempo text (80), 120 at the second (60), and 80 at the third (144).

Furthermore, the above now is also messed up in the main score.

The tempos are fixed by saving and reopening the score.