[trunk] Changing actual duration does not work for full measure rest

MuseScore trunk - r3530

1. Create a new flute score in 4/4
2. Right click the second measure -> Measure properties -> Change actual duration to 6/4
3. Enter 10 quarter notes from the start

Expected result : the two first measures should be filed. The second measure with 6 quarters
Actual result : the second measure looks like a regular 4/4 measure.