What I expected to happen was...:
I would of had moved if the boat was on a rail.

What actually happened was...:
I tried moving in 15w46a, it didn't work. I then tried in the latest official Minecraft version "1.8.9" and it worked successfully. Here is a youtube video explaining ALL evidence of the bug: https://www.youtube.com/watch?v=IloBsspSA6M . I posted this link because the video file is too big to attatch to this.

Steps to Reproduce:
1. Place a rail down.
2. Place a bot on the rail.
3. Try moving. (It won't work, but will in 1.8.9 as of now)