Key signature appears in multimeasure rest after being deleted from underlying measure
True in 3.0.5 and current master:
1) default score, or new score from treble template with system break after measure 4
2) add notes to measure 4
3) insert key signature at measure 5
4) "M" to enable mmrests
5) "M" to disable them again
6) delete keysig
7) "M" one more time
Result: keysig is back
Note also you cannot delete the keysig while mmrests are enabled, even before triggering this bug. That is, you should be able to delete the key signature form the mmrest after step 4, but you can't.
Key signatures are not current not linked between the underlying measures and the mmrests. Same with time signatures and clefs. There are a number of other subtle problems that could be solved by linking these - the non-generated ones, anyhow.