I was trying to leave a comment on someone else's WordPress blog, using a secondary email address. It claimed that email address belonged to a WP account, and invited me to log into that account. I tried logging in using that email address, and failed. When I tried to reset my password, and supplied that email address, it said there was no such user--i.e. I can't comment without logging in because the address is associated with a WP account, but I can't reset the password using the address because it isn't associated with a WP account!
I (obviously) do have a WP account, but my secondary email address isn't listed on it. It *is*, however, listed on my Gravatar account (which also shares my primary email with WP). Could it be that having my secondary email on my Gravatar account is preventing me from commenting without logging in, but because the address isn't on my WP account, I can't log in to comment either? If not, what else could be going on?