Given the rotation test results, I would agree that you've got bad detectors.
Thanks for coming back to give us the update. Keep us informed. It's always nice to get that final data point on a problem.
It takes an iron man to play with a toy iron horse.
i don't have my instructions for the dallee detectors handy but i remember reading about a trim potentiometer that adjusts the units sensitivity. you may have to adjust it to desensitize it a little. i've got three detectors in use for about 8 months now and they work good. very sensitive for n scale as they trip as soon as one wheel of a loco spans the insulated gap. if this doesn't work call dallee. they may be under warrantee.
Have you tried contacting Dallee on this? It sounds like you've got a problem with the circuit. It's not likely to be the detector.