You mean they reverted to their natural diet?
If so, that's no surprise.To me, what would be surprising is to find anyone who has successfully kept one fat and healthy, on a non SPS diet. Not here to start a fight, but the video would clarify plasticgoat's position.
I'm more than happy to be proven wrong, but I don't think getting them to eat non coral foods in small amounts is such a big deal. If the butterflies are freshly caught and in a tank with several other chaetodons they will peck at the odd frozen mysis etc that the facultative corallivores are eating. I have seen this at my LFS.
But getting them to enthusiastically eat enough of this kind of food to maintain them in the long run... Well, I dunno....