AFAIK, this button is called "CWS" for "control wheel steering" on the big birds. At least it was labelled CWS on the 737 simulator on which I did my multi-crew training many years ago. It does not really deactivate the autopilot, but only decouples the autopilot servos while leaving the autopilot running in it's current mode. When the button is released, the autopilot will resume as if nothing had happened.
On "my" TCS-button equipped aeroplane, it also sets the autopilot to the current pitch/VS/speed/bank values when in pitch/VS/FLC/roll mode. I do not remember, if "CWS" does that also.