Great suggestion!
12v AC.
So I disconnected the three wires at the switch machine, and used jumpers to an adjacent machine. No bounce back, although, a few times, the jumped switch didn't throw at all--could be a jumper connection thing. Seems the DZ-1000 is okay. Maybe the 2-button controller is the issue?
I do have both these switches wired for the non-derail feature, both have worked for several years. This testing has been with the 2-button controller, not cars on rails.
I may have a spare DZ 1002 controller to try next.