A couple of thoughts, I have an old Reloader Special (forerunner of the Rockchucker) and I found that if it isnt mounted to a very solid surface the extra vibration causes the decapped primers to bounce erratic, sometimes out of the catcher.
During the decapping operation the plastic primer catcher works its way forward causing a large gap between the inside edge of the catcher and the press letting the primers fall through. Take a large rubber band and rap it around the catcher and the press to keep it in place.
No matter how solid the press is mounted, how tight the catcher is held to the press,,,, keep the broom handy, a few primers on the floor is the rule not the exception.
