Ok, here we go: my symptoms were not that krass as those of Nick_S, "scan queue overloads" I only got if I really overdid it
But I could not really increase values anymore for they jumped back down to very small values. J?rg's page explains in all length, that he simply soldered two small capacitors over pins of the rotary controler - for me as an electronics no big deal. So I just soldered directly onto the PCB two 330nF ceramic caps and *yatta* no jumpyness anymore!!!
Link