We had a problem reported from a Yahoo user unable to login to our site with OpenID.
Our records show that he first logged in 2 weeks ago, and his identifier was of this format: http://me.yahoo.com/username#abcde
When he tried to login yesterday, his identifier was of the random 24-character variety.
Since our system doesn't allow multiple users with the same email address, he was unable to create a new account with this new OpenID.
The obvious answer is that he has multiple OpenIDs and selected the wrong one to login with. But he sent us a video of his screen while trying to log in, and the Yahoo OpenID approval page did *not* have the dropdown list for selecting from multiple identifiers.
It appears that the identifier got changed somehow. Should that be possible?