ATM question for science buffs

This from a co-worker. Personally, I’m stumped.
“My ATM card never works in the debit card readers at the
supermarket. But last night, after I swiped it through
unsuccessfully five or six times, the cashier said, “Let me see it a minute.” She wrapped the whole card in a plastic bag, pulling the bag tightly over the edge of the card, and then ran the bag-covered card through the slot. Worked like a charm. She didn’t know why it worked.”

Amy ideas?

WAG #1. Her card stripe was scratched and it scrambled attempts to read it.By covering the stripe with a thin layer of plastic (as the scratch normally would be) it enabled the reader to make sense of it. (IMO, most likely answer)

WAG #2. There is a microswitch inside the reader that senses when a card is passing through and your friends card was too thin to trip it. (I doubt this one, but it’s a possibility)

WAG #3. Your friend was swiping too quickly , the cashier swiped slower and the bag had nothing to do with it.

I’d go with #1 or #3. The cards are manufactured to very precise international standards – sadly, I once had a (temporary) job measuring the height of the embossed letters on bank cards, and I had to read all of these damn standards.

I would have guessed #2. I have the exact same problem with mine–but here are the qualifiers:

  • previous debit cards were never a problem, only my latest replacement, so I can’t believe that somehow everyone became to stupid to correctly swipe the cards

  • the card has NEVER worked well in these situations–from day one. So it’s not that it was scratched or anything; it was f’d up when it was brand new.
    My pet theory has been that this latest card is just minutely thinner than my last one, and so, in some readers, does not have enough bulk to press the magnetic stripe firmly against the reading heads. Adding the plastic bag increases the girth enough to ensure it stays in constant proximity. Still, just a WAG.