Interface doesn't work correctly with two new scores in different key signature

When you create two new scores with different key signature, lots of functionnalities in the second score doesn't work correctly or even at all like:

• Arrows keys/dragging to change notes doesn't work
• Enharmonic respelling is broken (but still emits the correct note)
• Notes cannot be deleted with del key
• etc...

The first score isn't affected. Creating 2 scores with same key signature doesn't seem to trigger the issue.

How to reproduce:

1. Create a new score
2. Enter some notes
3. Create a 2nd score with different key signature
4. Enter some notes in the 2nd score and try to delete one note of it

Note: sometimes you have to create 3 scores to trigger the bug.
Commit: b7dde41
Edit: tested with c65ab20 but needs 3 scores and switching between scores stops the bug.