ONE oreder sent TWO charges to paypal

As enable of PayPal Website Payment Pro, in checkout page, when click "Confirm Order" button, it works, but it does not go to confirm page and still stay this page, press "Confirm Order" button AGAIN, then it goes to confirm page. In dashboard you can see order there, but check paypal account, there are two transactions over there with two different transaction IDs for same customer and same amount. Anyone knows the reason, pls?

Then select Transaction Method as "Authorization" instead of "Sale", paypal shows two authorizations with different transaction IDs.

Looks click "Confirm Order ", opencart sends charge to paypal rightway, so click again, sends second one.