Sounds more like the face plate needs a little nudging up, once had it happen on a .5 pre-amp.
Tom, you may have just put the front on slightly off center when you did the switch, very easy to to do if you tightened the the little nuts without the dial in place first.
Just do a visual check to see if there is a slight clearance at the bottom, top or sides of the dial, if so, try giving the face plate a light tap from the opposite direction, maybe with a paperback or something similar, otherwise you may need to remove the cover and loosen the nuts again but with the knobs attached to check clearance.
Robert