My blog lets people comment by leaving name, email, and website (optional). A user recently left a comment with his Blogger blog URL in the website field in the form http://<account>.blogspot.com . After submitting the comment, he was redirected to the Blogger OpenID sign-in page, although there is no reason he would need to sign in with OpenID. Other URLs in the website field do not exhibit this behavior.
I think this might be related to the comment verification algorithm that involves a call to the PHP method gethostbyaddr() that would be checking the blogspot.com domain, but I'm not certain. Does anyone have a clue about how to fix this?