Credit card expiration date shown in review step

I enabled the module and added a payment gateway and then added that gateway pane to the payment step in the checkout flow.
When I go to checkout it asks for the payment method (only Paytrail shown) and personal details, fine.

But when I click myself to the next checkout step I get a PHP notice and see text "Expires 1/1970" in the payment details. Looks like it might be credit card expiration date but no such information was asked at the previous step?