LEDs don't take much to light. Is there a ground leak going on when the multiple phase featue lamps?
I noticed an interesting effect with lamp driver boards. If you have a special lamp driver board with loading resistors, but you don't hook up the feature lamp bus to the loading resistors. Non lit lamps get a leaking path to ground through two resistors and an adjacent turned on SCR. You don't see it with incandescent bulbs, but LEDs will ghost. It also causes problem with the expander boards that use a lamp to turn on a motor or bank select solenoids.
I wouldnt be surprised if an SCR's pair light ghosts with LEDs and multi phase feature lamp power. The loading resistor trick will also not work on these multi phase lamps too. You would get both lamps turning on at the same time (right?).