Item Frames Breakable in Adventure

Item Frames Breakable in Adventure Mode

I thought the item frame would be unbreakable

I could brake the item frame

1. Put an Item frame on a block
2.(optional) Put a block in the item frame
3. Type /gamemode 2
4. Break the Item frame

P.S. I know that the item frame is an entity, but I am not sure whether it is a bug or it is meant to be breakable.