I was messing around with boats, then happened to break one whilst sprinting and my sprinting stopped. Further testing showed this also happens with minecarts and in survival mode.
What I expected to happen was...:
To continue sprinting on my merry way (Christmas tomorrow )
What actually happened was...:
My speed faultered, and my sprinting ended.
Steps to Reproduce:
1. Place a boat or minecart.
2. Begin sprinting.
3. Run at the boat/minecart and break it (make sure not to HOLD down the LCTRL button)
4. Notice how you are no longer sprinting