When you press the steady bottom (Defult "C") and shoot the rifle will push it self to the right and you cant move it back. It is most a problem when you are using a weapon with more than 10 rounds.
EDIT I can confirm that all weapons are affected.
Video: https://www.youtube.com/watch?v=ewc2EGPsmSA&feature=youtu.be
Just place down a weapon with a bipod and deploy it, see were you can look and start shooting it will move the gun to the right and you wont be avaible to move it back unless you exit the bipod mode and reposision.
The bug is there for any weapon you dont need a bipod, just hit "C" and start shooting it will show the bug regardless. But at the time I made the video I thought it only was for bipod but after more testing I can confirm that it is for all weapons when they are deployed on the ground.