Have you tried deleting the entry for the site in Keychain?
safari fetches passwords from its forms autofill database. In Safari, go to preferences, passwords. Find and DELETE the offending entry. QUIT SAFARI. Relaunch it. Check it again. You may find it again when it didn't show up after delete. If so, delete it again. Repeat until safari truly has forgotten it.
keychain access and apple remote desktop both have problems with getting duplicate entries into their heads, where it shows you the first entry (only) and
uses the second. So you have to delete it. quit. relaunch. delete AGAIN. (sometimes more than once)
