Hello Adrian
Thanks for your detailed feedback (if all issue reports were like this, my life would be easier!).
I agree that this animation is misleading, but we have no plan to fix it. Indeed, the iceScrum UI is now a bit dated and while the technology we used at the time was the very best available, there are now much better tools to build good UI/UX. Thus, we currently focus our efforts on the development of a brand new UI for iceScrum, alongside with other improvements. It will be released under the name «iceScrum R7».
I can give you access to a private Alpha version of iceScrum R7 if you want to try it and provide your feedback on the new interface.
In the meantime, I would recommend that you ignore the animation and only take into account the final state: if the story is not in the Sandbox and has moved to the backlog then it worked.