Jazzman, Do the trains your running have tethers?
My railking proto 2 F-3's had the tether port on the lead engine installed upside down so that the soldered wires hung down, after a period of time, the insulation wore thin and the wires would contact my fastrack switch frog, and the train would derail. I turned the tether ports 180 degrees and have not had a problem since.