Why does using an ideal torque sensor on differential of the 4WD Vehicle Model Example affect the simulation?

By adding in an extra ideal torque sensor to the differential of the vehicle model, it changes the output velocity: I thought if the sensor is ideal, it doesn't affect the model, simply relaying the input signal to an output scope.

I have attached both velocity scope outputs when the torque sensor and scope have & haven't been commented out to demonstrate the difference.

Can anyone please correct any flaws in my logic but also show how I could measure the torque on the differential without changing the velocity output.