On a Rev L (Ver 5.0) TIU both Variable Channels are being used to power alternate power districts on a loop of track. Each track district is isolated from the others with only a single DCS input to that district. Each channel draws power from one side of a Z-4000. DCS works fine on the entire loop ; however, while conventional operators can control voltage to both districts using the handheld they cannot control Whistle, Bell and Direction in district powered by 2nd TIU variable channel. The "All" Variable Channels option was used to program the Handheld. Thanks.