When in a boat with a mob or player and you try to break a block in front of you, you actually hit the mob or player that is behind you in the boat instead of the block you are aiming at.

This may be related to this, but if you have a horse in the boat with you, your control hint constantly shifts from nothing to LT-RIDE, blinking on and off very, very fast. Also when you put your horse in the boat and then attempt to get in, you have to find the "sweet spot" to have the control hint switch from "Ride" to "Board" as it is always trying to get you to ride the horse.