Can this be related to the fact that MPCs support MIDI capture?
If you get some sound coming from a note not included in the clip, then (I guess) Bitwig needs to play that MIDI internally somehow, it cannot just produce the sound “left” by the time the clip starts. Maybe we could move this discussion to Drafts and then link this request with MIDI capture?
Still about the MPCs (I have an MPC One btw, hi) 
another factor to consider is that very often notes trigger samples, not the sound produced by an instrument. Technically this is a very different problem, I believe, because rendering a piece of audio at a given time can be dine without having to play the sample from the beginning.
In other words, have you tested whether this MPC feature works for their synths too and not just for samples?