This is happening with a fresh install of OC 188.8.131.52.
When testing the PayPal Pro payment extension, after clicking "confirm order" the "please wait" notice shows up and nothing happens after that (the user isn't redirected to a success page). Checking PayPal confirms that the payment was successfully processed.
The lack of a redirect of course allows the user to then click the confirm button again, thinking the first attempt failed, and submit multiple payments.
Looking at the console in Chrome, there is no activity after:
XHR finished loading: POST "https://domainname.com/index.php?route= ... p_pro/send".
Thanks for any insights!