I just tested again - in two different browsers, Firefox and Safari. No scroll bars.
The popup stays on my screen for about 2 seconds***. Whatever, even 5 seconds are not enough to see and analyse all HTML - so much should be clear, or? 2-3 minutes are minimum, I'd say.
But what for, you don't have a problem, there are no scroll bars. Sure you have no caches showing you "old stuff"? Clear them.
*** That's maybe what's left over when considering what happens after clicking "add to cart": appr. 10 secs "connecting...", another 6+ secs transferring before page refresh is starting, another 4 secs before the content in the mainbody starts appearing, then 2 more secs before the popup is there - for the blink of an eye. Could be server, could be connection, but so it is. Probably nothing to worry about if your customers are all in Oz.