All a user of his line has to do is hit the feature access codes set up as system wide parameters and SAC gets activated. I would try to remove the bridged appearances of his number and see if it still happens.

Also check and make sure his buttons are labeled right on his phone. It could be labeled one thing and he is hitting it. Disp sta xxxx.

Mike Jones
"A people that values its privileges above its principles soon loses both."
- Dwight D. Eisenhower (1890-1969), Inaugural Address, January 20, 1953