OK.. sounds like you have either a bad connection or have a stray voltage riding up the ground.

get an alligator clip and attach it to the 0V point on the transformer.. then measure the ground to the dull lamps.. it should read 0V ( no potential difference)... my guess is thats its reading 4 - 6v which means you have a lamp voltage from another source shorting the the ground on the dull lamps