It might be customary at that resturant to share with the kitchen but this is your first month isn't it? It's possible, depending on the time frame, your boss took money for the kitchen from you and plans to give it to the on their next payday? I'm just guessing, here.
You could ask your boss why the kitchen is bitching about not getting their money, go to the boss with the kitchen help, or just tell them to see the boss.
Or take a shotgun to work and watch 'em sweat.
