I'm writing as a user of a WordPress site who has encountered an error
that I've narrowed down to a WordPress.com cookie. The site is
http://nordicxplained.wordpress.com/. Under the Media tab there's a
drop down menu. In Opera, currently 12.12, a WordPress cookie is
causing the drop down menu to start two lines down, which makes the menu unusable.
To find why this was occurring, I did a clean install of Opera and then
added the previous user files one by one. The problem appeared when I added the former cookies file. First, I eliminated all the NordicExplained cookies, which didn't solve it. Then I eliminated all the wordpress.com cookies and the drop down returned to normal. To narrow it down, I eliminated those cookies one by one. The highlighted cookie in the following screenshot is the culprit: http://i45.tinypic.com/oayb11.jpg.
I posting here assuming that the site holder has no control over the cookie at the level it would cause an error. Since I have not tested this with FF or IE10, I don't know if it's browser specific. In case it is, I'm also reporting this to Opera.