Psychtar question

[psiico]

Does anybody know exactly what's going on inside a psychtar pedal?

Here's why I ask, when I play for example an open a and then another a (2nd fret) on the g string, no problem, both notes ring out.  When I play the open a and say a g (12th fret) on the g string they seem to cancel each other out and both notes die really fast.  Is this a phase thing or is something else happening here?  I noticed in another thread about impredance someone saying how the magnetic field from pickups and strings interact both ways, could it be that something to do with the psychtar causes the pickups to dampen the strings if two mismatched notes are played together?  Fifths and octaves are fine, everything else has this effect.  I should add that I've noticed if I record the guitar tracks seperately there's no problem.

Here's a recording with one guitar, note how terrible some of the note combinations sound:

http://media.putfile.com/sitar1

Here it is again done with two seperate guitars.  There's also some drums, sorry about that, I'm writing a song and this is a possible intro idea.

http://media.putfile.com/sitar2

It's not so much that I'm looking for a fix, I don't expect there is one, I'm just curious and trying to learn something.