Yeah, UA has had a lot of trouble communicating how purchasing air travel works. They tried adding a multi-paragraph disclaimer to their Web site and forcing you to read and acknowledge it before you could enable the "expert mode" that lets you see fare classes, but either their wording was unclear or people just did not read the wall of text that said "published fares and fare class availability are two different things, please understand that and don't swamp our call center with complaints that you see L availability but can't buy an L fare."