Changing the duration of the initial whole rest in a measure may jump the current position.
This problem developed back in 3.6 or maybe even 3.5. However, with 4.0 pending, I didn't report it then.
Steps to reproduce:
1. In a multi-instrument score, in an empty measure not measure 1 and not part of the first instrument, select the rest. Click a number to shorten the duration of the rest (e.g., 5 for a quaver).
2. Note the focus. It should be on the new rest. It may be in measure 1 of the first instrument or it may be undefined.