I'd see it as an exception- every rule has one. So would cause me no confusion whatsoever if my T let it slide for once.
However, I am pretty good at respecting others boudaries - in my mind its a precaution. Stg along the lines of if I'm gonna recpect theirs they would respect mines.
Plus my T too has very few ones- no double RS, respect the time/place/payment of the sessions, no physical violence in sessions and to call his cell only if SUI (he only switch it off while in sessions- so clients can call him nights/ weekends). When we talked about it he said that he sometimes needs to establish more strict boundaries with some clients who -how to put it- struggle to maintain them in a healthy way?