Is this one continuous loop of track?
Are you using a 50-1014 - 12 position terminal block? Using a 50-1020 is different. Each bank is Hot and Common - one high and one low - although the input terminals would give the impression that they are separated like the 50-1014.
The key points of isolation are where the 11 - block power district begins and ends adjacent to the 12 - block power district. Remove the variable #2 hot wire from the Z -4000. Power the variable one and check for voltage on the track. It should only be in the 11-block power district. If it is on the variable #2 district, there is a wiring issue.
