That's strange indeed. I've read in several travel books and was told from locals. And when we passed monc kids at the side of a river whith a boat and some people made photos they started throwing stones towards the boat. I took that experience as a proof what I've been told. Hm, but your contrary experience puzzels me. Now I am confused.
Very strange they posed for you.
Never heard of that law. I'd lived there for more than 10 years and never heard once.