The Mopho goes to the screen for whichever parameter is being edited. So if it's going to the low pass filter screen, it thinks that parameter is being changed. This suggests that something could be wrong with the potentiometer.
If there's dirt or moisture in there, you may be able to clean the pot by twisting it rapidly back and forth, through its entire range, several times. If that doesn't work, potentiometer cleaner is available at electronics stores (Radio Shack, etc.) or online (for example,
https://www.amazon.com/Hosa-D5S-6-DeoxIT-Contact-Cleaner/dp/B00006LVEU). If you do need to resort to cleaner, it might be necessary to open your Mopho up and apply the cleaner from the back, but this is really easy to do.
If it's still giving you trouble after that, you might need to contact DSI.