I don't know, Moose. Lip twitching is something that people can get from innocent causes, even such as caffeine. Do monitor it carefully, though, and let your psychiatrist know asap if it persists. If it's the Haldol, I wonder if it's a dystonia or similar. I once had brief involuntary lip puckering from Navane (thiothixene), which is also a 1st generation antipsychotic. It stopped when he lowered my dose.

I remember in my youth having a frequent twitch just below my eye. It was weird. I felt it and saw it clearly. I have no idea what caused that. I had never even taken medications at those points.