Some detective work revealed the source of the errors.
The dye used in the blue punch cards was slightly hygroscopic.
The absorbed water made all the blue cards slightly longer than
the rest, just long enough to throw off the reader.
Years ago, in the book "Steal this Book", Abbie Hoffman
suggested that anytime you end up with a punch card, in
order to be a troublemaker, soak the card in some solution
that, once the card is dried, has cause it to shrink
uniformly so that it will jam the reader.
As you can see, he wasn't much of a "fan" of "the system".
-dq