Instrument swap corrupts time signature

following topic https://musescore.org/en/node/92616

Issue confirmed on 2.0.2-stable and with Nightly c012358 on Win7.

Minimal reproduction steps:
1. Create new score with non-4/4-compatible time signature (so not 4/4, not 2/2 either). A different amount of beats per measure is required. Used 7/4 in the attached example.
2. Press `I` to open the Instruments dialog
3. Add a new instrument (doesn't matter which one)
4. Remove all existing instruments
5. Confirm
6. Score is now in a corrupted state. Time signature is missing on the new instrument.

When 'Ignore' is pressed on the corrupt message, the score opens and by attempting note input, one can verify that the measures themselves still have the correct time signature, but it is in effect the time signature itself that is missing.

It only seems to happen if you delete all existing Instruments and add the new Instruments in the same action. So a workaround is to first add the new Instruments and press OK. Then re-open the Instruments and remove the old Instruments.
You'll notice the time signature now being present on the new staves as well.