The summary on Wikipedia says: "The SCRAM was started when the EPS-5 button (also known as the AZ-5 button) of the reactor emergency protection system was pressed: this engaged the drive mechanism on all control rods to fully insert them, including the manual control rods that had been incautiously withdrawn earlier."

I don't know if that's true or not, but it seems like it ought to be true from a fail-safe perspective.