Steps to reproduce bug
1. Create new score in 4/4 time
2. The first whole-measure rest should already be selected. If not click to select it.
3. Notes > Tuplets > Triplets
4. Press Esc to leave note entry
5. Click to select the third half-note rest in the triplet
6. From the note input toolbar select quarter-note duration

Expected behavior: Tuplet should become two half-note rests followed by two quarter note-rests

Actual behavior: Tuplet expands into the second measure. Edit > Undo removes all beats from the second measure

MuseScore version: r. 2883 nightly

(Operating System: Windows 7)