It's most likely the expression pedal (physical position).

I'll bet if you step down a bit more on the toe-down or heel-down position, the values will reach the correct minimum/maximum #'s you intially set.

It's happened to me before. The expression pedal I had lost the "weight retention" at the toe down and heel down positions. It was almost as if you'd push down to the toe-down, but physically it sprang "back" a tad bit which tend caused the M9 to back track in the value internally to the new physical position of the expression pedal's pot value.

You can try setting the maximum/minimum to the toe-down/heel-down positions but don't apply any force on the pedal. That might work.