Fixed joint in multi-body dynamics simulation

[alinjar]

Hi, I have imported a URDF of a biped robot into PyBullet. Some rigid bodies in the robot are connected by fixed joints. It is expected that the velocities of the link joined by a fixed joint would be the same. However, it is noticed that they are different in my model. Kindly let me know the reason for the same and how can I get rid of this.