What I expected to happen was...:

In single player as well as on a server, we try to shoot a bow and arrow while sitting in a boat. The entity (arrow) does not launch out of the boat. Even shooting straight up. It just disappears. We have also tried snowballs to the same affect.

Steps to Reproduce:
1. Put a boat in any water.
2. Fire a bow/arrow at target.
3. Throw a snowball at a target.

You'll notice it never leaves the boat.