I don't know, playing w/the thumb on the same string as the fingers seems awkward to me, I've never heard of this. I have a Paco de Lucia dvd and I know he doesn't do this. I'm pretty sure this is not done in traditional classical music either, since it is my understanding that classical guitar players use the fingers for strings 1,2,& 3 and their thumb for strings 4,5,& 6. It would be interesting to hear from Azreal on this subject since I know he is pretty up on this stuff.