Zerberus: region containing identical "group" and "off_by" values doesn't play

Observe the following region:

<region> sample=saw.wav group=1 off_by=1

The correct behavior would be that each note played would silence all other notes that are still playing from the same region, essentially behaving as a monophonic (only one note playing at a time) instrument.

However, this region in Zerberus doesn't make any sound at all! My guess is that the region silences itself as it is starting rather than only affecting samples that have already been playing.

I have attached a test project that should play a melody using monophonic sine wave. Directions are at the top of the included MuseScore file.