When going fast in a boat, then exiting, your hands become invisible, like when going fast in a boat, plus every right-clickable item in the hotbar becomes locked. You can break blocks with items, however not eat, attack mobs or shoot an arrow from a bow, etc. Neither can you reenter the boat or open/close doors. A fix to this problem is to exit to the main menu, then to rejoin the world. Its a small, but annoying bug.