Originally Posted by Kimmo

One thing that can really complicate matters when trying to adjust a disc caliper is if the mounting faces and/or bolt holes aren't dead square... you line up the caliper just so, and then when you tighten the bolts, one side of a bolt head grabs first, and the caliper moves no matter what you do.

It's a bastard. And I've come across it on some nice bikes... hopefully that was just an initial hiccup as manufacturers adopted road disc and they've got on top if it.