When exiting a boat onto land, the boat and any mob inside of it will sometimes disappear. The player is still standing on top of the boat, and will vibrate and move very slowly. Other mobs that touch the invisible boat will do the same. The boat cannot be broken. 

After saving and quitting and then reopening the world, the boat with the mob in it reappeared. 

This bug occurs about once every 10 times I exit a boat. It can occur with or without a mob in the boat.