> I'd be somewhat willing to bet continue to stream audio is also a quality assurance mechanism. Some networks will shape traffic according to load. A quick jump in bandwidth can introduce unexpected jitter and latency. By continuing to stream audio (but not necessarily process or re-transmit), video conferencing can better ensure an un-interupted experience.

They don't have to actually send the data though in this case they should just send 0 padding. It's all encrypted presumably, so the only externally observable factor is the packet size.