Opera before 11.65 does not ensure that the address field corresponds to the displayed web page during unusually timed changes to this field, which makes it easier for user-assisted remote attackers to conduct spoofing attacks via vectors involving navigation, reloads, and redirects.
http://www.opera.com/support/kb/view/1018/
http://www.opera.com/docs/changelogs/windows/1200/
http://www.opera.com/docs/changelogs/unix/1200/