This is classic problem, Robicon drives from the 1980 -1990's would burn up the transformers the same way. The generator testing the load induces voltage on the lines. Older generators pump out pure wattage "no regulation" so any load on the system would be resistance example" the Brake Pre torque settings". We put fuses in brake controller circuit. that way if the genny is" out of phase" it only fries the fuses.