Respironics Auto-BiPAP Constant Pressure Glitch

I've been noticing an occasional glitch in pressure with my new Respironics machine in BiPAP mode and set with constant IPAP and EPAP pressures. It only seems to happen when I'm about half-awake and breathing regularly. I'll incidentally change my breathing abruptly, like puffing through my nose or something and the machine responds with what seems like an abrupt momentary pressure vacuum which jerks the hose around as well as tending to awaken me somewhat.

It's taken me a while to decide that it's actually the machine, as opposed to some other cause, but it definitely is a machine response to my abrupt change in breathing. I've wondered whether it's tied in with the safety relief valve in my Ultra Mirage FF mask. On a scale of 1 to 10 it rates about 0.05 right now in terms of affecting my sleep, but as I get more used to the machine I suspect this might become annoying at some point.

Anybody else experienced this sort of thing with an xPAP machine, or know what mechanical mechanism in the machine causes this to occur? Does this sort of thing occur in other xPAP machines? It strikes me that it might be a minor bug related to the newness of the Auto-BiPAP.

Regards,
Bill