You would need to measure the actual position of the shaft and the commanded position of the shaft to see the lack of torque during microstepping.
From the Faulhaber site:
What Does It Mean? The consequence is that if the load torque plus the motor’s friction and detent torque is greater than the incremental torque of a microstep, successive microsteps will have to be realized until the accumulated torque exceeds the load torque plus the motor’s friction and detent torque. Simply stated, taking a microstep does not mean the motor will actually move. In summary, although Microstepping gives the designer more resolution, improved accuracy is not realized. Reduction in mechanical and electromagnetically induced noise is, however, a real benefit.