Mine would act stupid on occasion. I would unplug it for a couple minutes and plug it back in and it seemed to reset itself. I sure wish the Ultrex would hold 1/2 as good as the Xi5 but I sure like the foot pedal.
How bad is it holding? If you've made adjustments and it still isn't holding well, you might want to have it checked out. My spotlock holds at least as well a XI5 if not better. Make sure you don't have something around it that is interfering with the signal.