Wow, this was super helpful. I just ran into this same issue on a board I spun for a custom joystick. Thank you for diagnosing it and saving me a TON of head scratching.
For those of you with a single axis system: Is there a trick to using the VPForce board with only 1 motor? I can only get the software to show motion when I have 2 motors connected. The software says the motor is detected but never shows motion. If I attach a second motor, both motors work perfectly?