Easiest to see on the casual walking animation (As it's very long).

1. Switch to walk (default W+S). Have your weapon raised.
2. Walk forward.
3. While walking forward, double tap left control to lower the weapon.
4. Release all controls.
5. Notice you walk forward for about 5 meters automatically.

Do the same for other animations, and you'll notice the same happens for all of them (Albeit a lot less, because those animations are shorter).

Eg. walk backwards, then lower weapon. Or walk forward and raise weapon, etc.