I've got this problem as well.
We stay almost exclusively at Marriott and I keep running into this over and over again. I've been put in rooms that they insist are ADA rooms and there is not even a way to get in the room, let alone use it. This was at a Courtyard. The manager refused to take that label off of the room, saying that there must be a reason it was labeled that way in the system.
I sometimes feel that the designers are actually hostile to wheelchair users. How else could they come up with some of these design flaws? I stick with Marriott because we are platinum and it doesn't seem to be much better anywhere else.
I NEVER count on my online reservations being correct. I call the hotel directly and ask to speak to the manager, after I've reserved. Then, the day before I arrive, I call them again. Even with that, I've been given the wrong room.