It is not always a PoS issue; it is, for the most part, a problem of EF, and it has been like that for a long time, with several posts on the subject. Specify airline X and get one result; run the same query without specifying any airline and get a different result for the same airline X. It does not happen all the time, but enough for it to be a real problem. Why EF has not fixed this after so long is something I don't understand.