Unison combines all four voices for one track only. In other words Unison is monophonic. One note four voices. What the original poster has pointed out is correct. When Unison is selected and all voicing enabled, checking ‘Use Track Sound’ should when focusing Track 1 play only track 1 in unison mode. Track 2, Track 3 and Track 4 the same with respective Track Sounds selected. I too think this is a bug and should be submitted.