Adventures in Scantron Voting

Some time ago, I lauded North Carolina's optical scan voting system, comparing it favorably to the touch-screen crap used in other parts of the country. Well, Minnesota has op-scan voting, and as this link shows, they're quite adept at screwing it up. Seriously, I didn't know there were that many ways to mess up filling in a bubble. I guess the Banditos Theorem applies here, though I don't think it requires that much intelligence to fill in a bubble. Does it? Is it that hard, op-scan voters?