This was answered via the internal ticket-based support system.
But for those reading, this is simply because of how the TB-3 operates...specifically.
The Roland TB-03 does not map incoming MIDI note velocity to output volume of the note - as the original TB-303 did not play notes of various volumes.
The TB-03 responds only in the following way:
If incoming MIDI note velocity is 0, note volume will be 0
If incoming MIDI note velocity is 1-99, note volume will be normal
If incoming MIDI note velocity is 100-127, "accented" not will play with special volume and filter characteristics, with depth of effect by the level set by the "Accent" knob.