Why is 'redirect to PayPal' notification shown twice?

[innato]

VM 3.0.16 on Joomla! 3.6.0 and PHP 5.6.
I did a search for my question but couldn't find it. I appologise if it is a duplicate...
After confirming a purchase, the message "Please wait while redirecting to PayPal" is displayed twice: one inside a button, the other somewhere at the left (js?).
Is there a reason why the same message is displayed twice?