I have these ribbon shaped stools since almost three months. It comes from rectal inflammation and swelling, my doctor just assured me today (I was worried about that, too). Although I do use Rowasa and Cortenema alternately (started again tonight while tapering off Prednisone), the ribbon thingies stick around for quite sometime. I haven't seen a normally formed stool in a loooong looooong time either.
So don't worry about it, I am in the same boat. Once the swelling in the rectum goes FINALLY down a bit, the shape thingies will disappear.