It's not just cleaners that do this. It's quite common to have to feed shrimp and any other fast-moving Crustaceans first and/or separately when feeding corals. Even hermits and emerald crabs can be a pain about it sometimes, although the results are often a bit more brutal then compared to what shrimp do. Shrimp can still kill corals though with too much picking. How prone the Crustaceans are to trying to steal food from corals and how determine they are abut it depends a lot on what their diet and feeding schedule is, although sometimes they will just get into the habit of coming over to stomp all over things wherever feeding is happening. If a good feeding schedule doesn't kick the behavior, you just have to offer them some of whatever you're adding and shoo them away. If there's food sitting by the coral, they will generally go for that and ignore the coral itself. For example, I have a few very well-fed CBS that will still be a pain and go try to steal food when I'm feeding corals in their tanks; I always have to give them some of whatever I'm feeding at the time to make them go back under their ledges.