As it was explained to me... the Discover card was processed as usual and the animated "processing transaction" (or whatever it says) came up and stayed up "for a long time". I have the timeout set at 600 sec. and it could have been ten minutes. Then the window went blank except for the "continue" button which was pressed.
Now there are times, when this happens, that the software seems to have hung up and pressing this button causes the printer to print the receipt and the sale is completed. In this case, the screen just went away and the sale was still open. Running the card again yielded a duplicate transaction warning and the charge was aborted (avoiding the duplicate charge).
The charge was completed but ezPos doesn't know that, leaving the transaction "Not Paid". I see no option to turn off Process Credit card in the payment window.