When a player right clicks any block (besides use-able ones like levers) it says this is protected.

[Anna Bakker]

When a player right clicks any block it says "This is protected!" even if you right click with nothing in your hand or a item you can't place, such as a compass.

It will not say this is protected with you right click a lever, crafting table, cake or anything similar (note: steps/seats do not count, so you get this message each time you sit down at spawn by clicking a seat).

This is most likely because it does the same thing when you try to place a block.