Hunger refills while walking or sprinting

My hunger is going down while im walking or sprinting then goes back to what is was.

What i was expecting to happen was.....
I was expecting hunger to act normal

What actually happened was.....
It refilled while i was walking or sprinting, then it went back to what it was.

Steps to Reproduce:
1. Walk or sprint in survival mode with difficulty at easy or higher and have hunger low. (not sure if it affects hardcore)
2. Watch the hunger bar.
3. Stop walking.