Falling Through "Weak Ice" While Standing On the Deck Of a Boat?!

Just as the title says, I boarded one of those larger boats that wash up after a storm, only to fall through the "weak ice" beneath the boat, while standing on the WOODEN DECK of the boat. How do I fall through ice when I'm standing on the deck of a freaking boat DESIGNED to hold people while FLOATING ON WATER?! Hinterland, please tell me that's some sort of bug, because that makes no sense whatsoever!