This bug started with the player vehicle changes in 3.1, it persists in 3.1.1 on live realms as well as the 3.1.2 PTR. I believe right before 3.1 went live someone said they would look into this, but 2 patches later it remains. This is a really annoying bug for bike owners, and in an effort to help get it fixed I made a video showing exactly how to reproduce this bug. I hope it's some help to Blizzard QA as they address this issue.

http://www.youtube.com/watch?v=06mzduwj22Y

Please bump this thread with confirmation if you're a hog owner that has experienced this.