Sometimes, when I exit a boat, it becomes impossible to push around, re-enter or break into an item. It just sits there. Sometimes if I quit and reload it becomes a normal placed boat, but sometimes not.
Also, I have occasionally had a boat break against a shoreline it's a good 10 blocks from. I'm floating along, minding my own business, and suddenly the boat vanishes under me and wreckage appears on the shore directly ahead of me.