I power two loops with one Z4000.
One thing I've noticed when running a train is when the occupied loop is set to 15 volts and the unoccupied loop set to 15 volts, when the crossover happens the now occupied loop drops to about 13 volts, the train slows and the now unoccupied loop the volts increase to about 17 volts.
For me to have a smooth transition from loop to loop I have to set the unoccupied loop about two volts higher.
Does this sound like normal transformer behavior?