Strange NL betting rule

[Strat6]

I ran into this at a casino recently and I still can't seem to get a straight answer from the card room people.

1/2 NL. I am on the button. 6 players see the flop at 10 each. Board comes with a Jh 6s Jd, giving me trips ( J-10). BB bets 15, next player goes all in for 21. I more caller before I raise to 100. But the dealer makes be pull back my bet stating that I can only call since $21 bet since any all in move that equals less than half a raise, i.e., $30, freezes the action for that round meaning that I could only call teh $21 bet. I protest but he holds his ground and makes me take my bet down. The turn is a blank and gets checked to me and I make it a hundred. Get called by the flush draw. And guess what hits the river.

It took me hours to hunt down the answer and although the card room manager finally said the dealer was wrong, several of the dealers still insisted the card room manager was wrong.

Is anyone aware of a general rule where an all in bet which does not amount to a full raise caps the action for that round?

Thanks.