I'm running a 1999 Parker fly into the helix, mag pickups in to the guitar input and piezo into the aux input. The cable is a stereo jack to 2 mono jacks. When in the stereo mode, where the outputs are totally separate, I'm getting a crossover between the 2 sets of pickups, even when the input is not part of the signal chain. I realise it is probably a bad cable or jack on the guitar side, but I thought I'd get an easy fix out of the way before getting the soldering iron out!