I had a very bad experience with ANA in SIN. I had a ZED tkt, issued on AA tkt stock, but the carrier indicated was UA. As usual, it said "valid any ZED carrier", but ANA refused to accept it without an "endorsement"!I tried to explain the concept of ZED over and over, and ended up with their ticket counter supervisor. I politely explained my situation, and he was gracious and said he understood the rules of ZED travel, but was insistent that UA "endorse" the ticket. UA, of course, said that was ridiculous, but ANA held firm, and in trying to get the endorsement, I missed the flight and ended up staying another night.