I think I was bitten by the same united.com bug a couple of days ago. I wanted to upgrade with miles and went that route on the web site, but when I clicked to confirm I was presented with an error page. After that the only options were to pay with e-certs, a CR-1, an SWU, or "other, paper certificate". I chose "other" and when I later tried easy-checkin I could only get a redemption certificate to present at check in. I called CS and they pulled the miles, but I still couldn't get a correct boarding pass and had to use in-person checkin. Not a problem since they had a record of the miles being pulled. (I printed a screen dump of my MP detail just to be sure, but it wasn't needed.)