I have been having this 'hanging featured image' issue for several months, it is extremely aggravating!
We have multiple websites, it affects some, but not others, all using the same theme (NewsPro by Gabfire)
It is NOT a ModSecurity issue for us (had security completely disabled), and not a plug-in conflict (turned each off and on), as others have indicated in other posts on this same topic (see http://wordpress.org/support/topic/theme-twenty-ten-since-update-set-featured-image-hangs?replies=7, and
Obviously people with various themes are encountering the same problem, so I have to believe there is a WordPress answer.
Has anyone else SOLVED this?? Can ANYONE help???