Continuity mistake: When Chekov sits outside the general store chatting with Sylvia, his left arm and her right alternate from entwined to un-entwined and back again as the shots change. (00:27:40)
Continuity mistake: On the bridge, watch Uhura. She goes from both hands on her controls, to left hand on her earpiece in a split second.
Continuity mistake: At the end, on the Bridge, when the warning marker explodes, Kirk's arm shifts position between shots.
Continuity mistake: When Scotty inhales the gas, the amount of smoke changes between shots.
Answer: After causing Norman to overload, all of the other androids shut down. The same could be said for the androids on the Enterprise.