@michael: Just to let you know, I contacted the engraver/arranger of the music. In origin this file was an orchestral score, I stripped out everything except the measures containing the problem (copyright). The arranger works with a 'base file' (a file with all parts, instruments and groupings in place) without any notes, opens it in the latest Finale and starts adding the music (on Mac). He created his 'base file' in Finale 2003 on Mac.
So the parts, instruments and groupings have to go trough a conversion process, which may cause the problem (although it would be a bug, but I understand you can't stay backwards compatible forever).
But since we have multiple files like this (and will have more of them in the future) I'm still hoping for a solution.