AMotor query

Hi, I have an AMotor set up in 3-axis user mode with axes (1,0,0)   
(0,1,0)   (0,0,1) locked to the global frame. On all 3 axes, FMax is set 
to dInfinity, Vel is set to zero, and ERP is set to 1.0. This motor is 
then connected between a body and the static world. If I add any contact 
joints to the body, then I see a torque being applied and the body gains 
angular velocity. I was under the impression that motors 'look ahead' 
and so with the parameters I have set it should be almost impossible to 
rotate the body. Am I misunderstanding how motors are implemented?

Cheers,
Mark