That's weird from my end this (Paypal Pro)does not work with one click , I have just tried it again with Explorer & Firefox and with both browsers I have to select "Pay Now" twice otherwise the payment does not go through, the first click just XXXX's out the credit card details, the second sends the details. If you do not click twice the payment does not go through.
I lost some orders through this yesterday as I was at a show so was unable to assist customers. One even submitted the same order 8 times without working out that if you clicked a second time the payment would work, hence I have had to put a note on telling them to click twice.