WK1 Midi problem

I recently bought a WK1. Love it! But I'm having one problem. So far, I haven't been able to get any MIDI output from the "lower" keyboard when the keyboard is split. I'm trying to run an external rhythm box (Salton TS4) using the left hand. I've tried changing channels on both the keyboard and the Salton. MIDI out works fine when the keyboard is not split. System date is 13-06-2003.