I think that we've pretty much figured out the condition now. It does not occur with new cases so I'm assuming it's the expanded (read bulged) cases that have been slimmed down in the sizing step.
If you are using RCBS carbide dies and have adjusted them as per instructions you will not resize the whole case. Between the thickness of the shellholder and the gap needed so the carbide inserts do not hit the shellholder and crack, it is impossible. It is also not needed. As long as the reloaded shells drop easily into the chambers, there is not a problem.