I've been having the same problem with my peppermint pair. They finish their food, then go to my candy cane and my duncan and rip the food out of their mouths too. One even took a chunk out of my candy cane one evening. If the bad behavior continues, I'll be attempting to trap the little rat bass turds. They did great until my tank was fishless (or mostly fishless, thanks to a certain nano blenny that I NEVER see). Then they commenced with the bad behavior. Now that I have a pair of firefish, I haven't seen the peppermint pair at all, so maybe they'll start minding their manners again. Good luck with your problem children!