Ok, tell me if I'm a total idiot here and never did see this one.
What I found in 2005, and also verified in 2004 & 2003, is that if you have a part in an assy mated to a sketch that is sitting there in the assy (skeleton) and you suppress the sketch, the mate is still active. This seems to fly in the face of the fact that suppressed parts also let go of their mates. They aren't destroyed, but they are not holding the part, either.
WT