I was recreating my encoder measurement set-up on my breadboard, but having significant trouble. I was just sticking copper wires into the motor ribbon connector. These wires were shaking loose and not giving good connections. I swapped-in some 2x and 1x headers and some Connectamundos and had a much more reliable connection. However, I still wasn't getting good numbers from my test software. It took me about 30 minutes to realize I had a floating ground between my MMB103 board and my breadboard. Once I connect their 2 ground planes, I was back in business. With this better test setup, I am finding that the encoders aren't that reliable. Supplying a short-duration (0.25 s) low current pulse to the motor and returning both motor leads to Vcc results in erradic counts: often little to no change in the count; sometimes the count is even backwards! I attribute this to back EMF: the motor is trying to overcome inertia and fight friction. The magnetic encoders are getting a larger back-current reading. A second source of trouble is when a low "leak" current is supplied to the motor leads. The output shaft doesn't spin any, but the encoders are counting away almost at the same rate as a full-speed spin. I can't explain this one.