I had a round look like a major overfill once (always look for a nominal charge before placing a bullet), and on investigation turned out to be the powder charge sitting on top of a crumpled bit of target paper inside the case. So now all the cleaned cases get examined under a good light and if I don't see the inside of the primer hole it doesn't go in the ready bin beside the press.
Always good advice. Also tumbler media can get stuck in the case as well, I've had that happen a few times over the years. - dan