Kind of makes sense though. If I had to do that I'd bounce the synth to an audio tracks, then see if the synth track and the MIDI comes over. I assume you meant Synth Track with a separate MIDI Track.
But come to think of it, I can imagine an Instrument Track might be even equally problematic (frozen or unfrozen). But again I never tried any of those kinds of projects, maybe I should dig some out and try it.