If mamagers could count

My husband and I went to Hennies on Sunday, and to his big surprise they had 1kg Eisbein on special, which is excactly what he wanted. When we ordered, the waiter told us that they were out of stock on 1kg Eisbein, and only had 500g Eisbeins left. Not a problem for us, as two 500g would make 1kg right? WRONG! They could not give us two 500g Eisbeins as it was not part of the special. My brain still breaks when I try to work out their reasoning.