Anacrusis creates time signature error and corrupts the file when removing the original instrument

If you remove the original instrument the score time signature doesn't carry over properly
As soon as I added the flute line and removed the piano score, the time signature turned to 1:4 (probably because I had the anacrusis set up for 1 beat).
The files will still open, and there seem to be ways to get around this problem, but it might be worth addressing the source of the issue within the code.

To reproduce this error:
1. Create a new score with an anacrusis.
2. Go to 'edit'/'instruments'.
3. Add a second instrument.
4. Remove the original instrument.
At this point, the time signature should change (or more accurately, shouldn't but does).

uploaded files:
anacrusis test ground 1 - created score with anacrusis
Anacrusis test ground 2 - changed original instrument, corrupted file.