What I expected to happen was...

When I happened to jump on top of the boat, I will be able to move normally, like I was only standing on to something.

What happened was...

I jumped on top of the boat (but not riding on it), then when I move in sideways, I tend to shake and move slower (without pressing the sneak button). 

Steps to Reproduce:

you may refer to the attached video/file

In case the video will not play...

1. Place the boat to any water surface.
2. Jump onto the boat, and no right clicking on it.
3. Move in any direction.