Blocked user interface if missing field on submit

In the checkout page, if the user clicks on “Confirm order” button but with some blank fields (for example the credit card info), then there is user interface blocking layer (a white transparent layer with classes “blockUI, blockOverlay”) that remains there forever, so does not let the user input the missing fields.

If user reloads the page the overlay disappear, but some users may not know what to do and abandon the purchase.