Two with bow connected notes play both if multiple identical voices

Env: Mac OS X Lion 10.7.5 (11G63)
GIT commit: a925ae0

I have some (choral) music where there are 2 voices in each staff. If the 2 voices are different notes, and each note is connected with bows, then if playing back it is played as one note with the right duration. That's good.

When the 2 voices have the same notes, and both voices are seperately connected, they seem to play back as individual notes.

Example:

In this example in the voices on the top staff the first 2 notes play as 2 seperate notes, while in the 2 voices in the bottom staff they play as one note (as it should be).

The complete file "Van_Oranje.mscz" is attached.