If you are experiencing issues with spent primers staying in the primer pocket after resizing you might want to check to make sure that the decapping pin is not bent or broken. You will also want to make sure your sizing die is properly installed and that the lock ring is firmly in place. Another possibility is that the spent primers are getting stuck onto the end of the decapping pin, and being pulled partially back into the primer pocket as the handle is lifted.
To correct this problem use medium grit sandpaper or a scotchbrite wheel to round off any sharp, square edges on the tip of the pin. This should allow the pin to punch out the spent primer without grabbing or pulling the spent primer back into the case.