Well, I believe the story goes back about 5 years or so ago; he use to do a lot of work on Sesame. However, there was a problem with him taking ideas from one of the other principal performer's notepad, literally swiping notes to an idea for a show and characters that this performer had been working on. When this muppeteer walked in on Rick reading his private notepad, well, you can imagine the awkwardness that must have been.
Needless to say, from that day on, he never worked there again.
Again, nice guy, talented performer, but not to be trusted.