Make individual beat rests when splitting a measure
Currently, when you "Slip a measure before current note," the result is 2 measures with measure rests. There is no indication on an individual part that this has happened and most (all?) scores use smaller rests to fill each measure as needed to show the two measures with fewer beats.
Both measures are also counted in the measure count, and one of them should automatically be excluded to prevent the measure count from being thrown off.