That's inevitable in the early days of a new system. It's not helped by the confusion in some shops where they have customer-facing card readers but still seem to need to take the card off you and run it through the till.
I think they should still do that, because the customer can get away with using any card so long as they know the PIN. Whereas under the old system, they had to sign for the goods and the cashier would have a cursory glance at the signature and the front of the card before authorising the transaction.
What's to stop a lecherous wife from taking his husband's cards and going on a shopping spree, since some couples, they tell each other the PIN of their own personal card when they're not supposed to. The wife will get away with it in this instance because assuming he hasn't noticed his cards have gone missing and it'll be made much easier because all she has to do is stick in the card into the reader, punch in the number and she's off. Plus, it'll give her time to destroy the card, rather than the store querying the transaction and retaining the card to prevent further use.