I've had the marching window box in the foreground often, even when the task IS completing in the background. I will have the confirmation email, seat selection, and upgrade requested, while the marching window graphic continues running on my screen until I just close it. It is definitely not connected properly to the software it's intended to serve as a "transaction pending" indicator.
When I get failed transactions, I usually wipe out all the cookies and cached pages from AC domains before I try again.