Other mistake: After Chekov goes beserk on the bridge and Dr McCoy and Scotty restrain him, Spock enters the scene and grabs Chekov by the sides of his face. His hands are close together as a human's face is around eight inches wide. When the camera cuts to Chekov's perspective view of Spock, Spock's arms are spread way far apart. Either Chekov's face has ballooned to over two feet wide or Spock is grasping the Panavision camera by its two sides. (00:14:34)
Other mistake: After the shot of McCoy checking Sickbay, there's a shot of Chekov. It was a quick shot but it can be seen that the film was run back and forth through about a second, as his movements can be seen to repeat rapidly in reverse and forward twice. (00:06:56)
Answer: After causing Norman to overload, all of the other androids shut down. The same could be said for the androids on the Enterprise.