That's not a bug, that is a feature!
But on a more serious note, we're aware of all 3p animation/grip bugs. Thing is we haven't had time to do proper animations for them, and up until about 3 days ago the experience either. I probably won't find time to animate the Piat for 2.3, but many weapons will feature new 3p anims for 2.3. Most prominent weapons first.