I thought I'd post this in case someone else runs into this issue. The problem is that Mach3 when combined with the newest ShuttlePRO hardware, Mach3 will "stick" when the outside ring is turned and the axis will continue to move even after the ring returns to the center. I'm awaiting a possible solution from Contour and I'll post it here.
Here is a photo of the "good" and "bad" boards. Externally they look identical.