The ref has authority over all the players and management from an hour or two before the game to the same time after, where ever they may be. Remember, Windass managed to get sent off in the car park after a game before. http://goliath.ecnext.com/coms2/gi_0199-9475128/Windass-banned-for-car-park.html I agree with you though, it is ridiculous.
In a world of common sense yes, in a world where the FA makes the rules no. The referee has the same authority during half-time as he does during play, and that means if it's something that would get NP sent to the stands for saying pitchside then it's the same punishment for saying it in the dressing room. Like I say, I agree it's ridiculous, but that's how it is. I still don't understand how Windass got a 5 game ban for driving past a referee in the car park and jokingly telling him not to give up his day job though, even if he'd been on the pitch and got sent off it'd only have been a 3 game ban at most.