Similar thing happened to me. The TSA made this big announcement that they were allowing cork screws, so I packed one in my carry-on. Going through security, an agent approached me and said I was carrying a knife in my carry-on. It wasn't a knife but the foil cutter on the cork screw. Needless to say, they confiscated it.

Upon my return home, I bought another cork screw, took it out to the garage, and ground off the foil cutter.

Next trip, the TSA again said they wanted to look in my carry-on, but this time they examined the cork screw and passed it as the 'knife' was gone.