I'm having continous problems with my tables saw fence (and older grey 2412) going out of square. I align it to the miter slot by losening the four screws at the base of the fence and squaring it up, then tightening them. After a short period of time using it, its back out of square by at least a 1/16". The back of the fence seems to be moving to the right for some reason. I also tightened the nut that controls how tightly the fence clamps onto the rails. Anyone else seen this problem?