Related issue and I think it suggests there is a deeper issue:

I am Silver. My partner isn't. He had 25K in his account that I would be using for a domestic ticket. (Since we collectively will use my account in the future for other trips, and he doesn't fly much so we figured to just wipe out his account.)

Anyway, I found a 25K award while he was logged in to his account. We entered my passenger information, and , so as to get to use breezeway, free bag check, I entered my SkyMiles number in the passenger info where requested. We put the reservation on hold

When we go back to purchase it a day later, I got the same information saying that the reservation was created using medallion availability, but it wasn't! We absolutely were logged into his account. I know this, because I HAD logged into my account, just for kicks, before purchasing the ticket to see if there was any imroved availability. There wasn't.

Still, the passenger info (mine) is correct, so we enter payment info , and try to purchase. The system says I need to call reservations. Reservations says that my partners account is not attached to the reservation. The CSR says all they see is my skymiles number.They "reattach" his number, and I am good to go and my reservation goes through.

So, I guess the additional issue I see, is that the computer system might also be thrown when a medallion enters their membership number, irrespective of whose account is being used to redeem the award.