i have two peppermint shrimp that were eating my mushrooms and frogspawn. i had to take my whole tank apart to get them out.
they were in my tank to eat an aptasia outbreak, they did a fantastic job at eating those. i had the shrimp in my tank for about 6 months with no coral at all. when i put the corals in there they started eating it like crazy.
maybe they were just bored of fish food. i have never heard of them eating corals before.
just thought i'd let you know my experience.