I have always had trouble with crown molding “slipping” on the miter saw, making for less-than-perfect cuts. I solved this problem by spraying the back of the crown molding, where it meets the wall and the ceiling, with a brief blast of spray-on adhesive within about 8 in. of the cut. The adhesive allows for a bit of grip against the fence of the saw so that there is absolutely no slippage and a much more reliable cut.
Matthew G. Michaels, Cordova, TN