I've not done it with the 1/4 round, but have you tried a simple 45 degree cut? When one of the planes is a stright 90 degrees you don't have a compound miter.
07:03PM | 10/19/00
This is referred to as an inside miter, the correct way to form this joint is to place the first piece into the corner with a square end cut. The second is measured into the corner of the wall and cut at 45 degree miter, then using a coping saw it is cut using the profile of the miter as a cut line. When making to cope cut you want the cut to be just over 90 degrees to the face of the piece of trim.