With my chip&pin VISA I observed that card terminals with additional customer PIN pad offer the DCC option to the cashier after entering the PIN even though the PIN pad displays the amount in PLN only. In Poland be suspicious with English text on the PIN pad display, e.g. AMOUNT PLN 150 ENTER PIN and check carefully what the cashier is doing on his terminal after the PIN has been entered.
Were the cashiers ready to press to accept DCC or did they honor the choice/give you the option? I've read Poland is very hostile in this aspect. Cashier claim ignorance or play dumb, "Well, let's see what happens..." and they know exactly what the outcome will be. I agree with
AllieKat that the payment networks need to step up enforcement with this issue.