I'm sorry but I don't see the measurements you are talking about in your plot because there are too many lines and no legend.
How are you setting the joint position? using the Motor
API or the Supervisor
Note that the Motor
API sets the target position, but the joint is not immediately moved to the target position.
Instead the movement from the current to the target position is computed based on the physics of the object and the Motor
specifications, like the maximum force/torque, maximum velocity etc.
If you suspect a bug, I would suggest you to post your project so that we can inspect it.
But note that Webots 7 is no longer supported, you should check on Webots 8.