Apparent corruption on copying a two-note tremolo across a barline

Ubuntu 14.04, GIT commit: d33f638

1) new score, 4/4
2) measure 1, note input: 6 0 5 C E (quarter note C & E on beats 3 & 4)
3) add two-note tremolo to the C (converrts to half note tremolo)
4) measure 2, note input: 6 0 5 0
5) copy the two half notes in bar 1 to beat 4 in bar 2

Result: score appears corrupt

It's not actually quite as bad as it looks - the durations are fine internally, and if you delete the tremolo marking, all is well. But it sure looks a mess.

I have a fix for this in conjunction with #49246: Some elements duplicated on time sig change since the code overlapsd, but am submitting separately in case it is decided to fix either of these a different way.