Since I work with polyphonic staves a lot, I have encountered the following problem.
In the 4 bars of the following picture, all whole notes have MIDI channel 1.
The quarter notes also have channel 1 in the first measure, channel 2 in the second measure, and then channel 3 or 4 in the third or fourth measure.
In the score editor it looks like this:
As you can see, the quarter notes are displayed correctly when they are set to MIDI channel 2. If they are set to channel 3 or 4, they will overlap with the whole note.
It would be good if this problem is fixed soon.