Magnus Modulus; LED help

[m-theory]

Professor Confused here, again.  I've built the Magnus Modulus, and it works, but I have to admit that I'm confused about the LEDs.  http://www.diystompboxes.com/smfforum/index.php?topic=72527.0

I understand that D2 handles the functional task of "tremolo-ing," but I'm confused about D6 and D8.  Are these indicators for on/off status of the modulation switch, because, if so, why two, and...mine do nothing.  What am I missing?