Yip, they can be a pain if the end of the wire has snapped. Unfortunately it's just a case of pursevering and getting something in behind the wire to flick it out as you turn the top head. I think I'd be inclined to pull the cylinder and lay it sideways in the vice so you can get a good steady continuous turn on the cap as opposed to small turns with cylinder insitu.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.