I have this router attached to a router table and make the height adjustments from the top of the router plate. It has worked very well in the past. But now, when I try to make height adjustments to the bit, the router drops down out of the notch into which it has been locked. This router has three height adjustment notches. It does not do the same when i take the router out and set in on its top. So something must be loose to allow the weight of the router to make the router drop. Any suggestions?