On the Open Beta build, it seems like the detection for when the mic is muted in-game is flipped for the "Voice" parameter. This does not seem to affect what remote players see, and I have had no issues that I know of for other parameters.

Screenshot 1: Intended facial expression when no mic input is detected

Screenshot 2: Intended facial expression when mic input is detected (to ensure blendshapes don't multiply each other and warp the face)

Video: Demonstration of both unmuted and muted behaviour. Note how wide the mouth opens on the unmuted demonstration.