[Trunk] Adding tie causes previous one to visually disappear

1. Create score.
2. Enter three F crotchets.
3. Click on first note.
4. Tie it to second note.
5. Tie second note to third note.

Result: Tie between first and second crotchet disappears visually. Tie again and the tie between the second and third note will disappear.

Using MuseScore 2.0 Nightly Build (4669) - Mac 10.6.8.