The exact same problem happened a month ago with iTunes purchases and also Disney. Coincidence? I think they just were caught red-handed, twice.

Amazon's policy allows them to withdraw purchased items [1]. It could be a bug, it could be policy, it could be a bug that exposed an existing policy. There PR has been, unsuprisingly, silent on this front. This is why I have no faith in digital ditribution; the music industry finally got it, the movie and game industry still don't get it.

[1] Availability of Purchased Digital Content. Purchased Digital Content will generally continue to be available to you for download or streaming from the Service, as applicable, but may become unavailable due to potential content provider licensing restrictions and for other reasons, and Amazon will not be liable to you if Purchased Digital Content becomes unavailable for further download or streaming. You may download and store your own copy of Purchased Digital Content on a Compatible Device authorized for such download so that you can view that Purchased Digital Content if it becomes unavailable for further download or streaming from the Service.

I agree. Pulling the purchased content makes no sense for Disney. If the general public is routinely exposed to the fact that digital purchases aren't "real", publishers will not be able to charge as much for them, since the value customers perceive will be lower (and that caps what the publishers can charge). Disney might pull future purchases from Amazon (which is apparently what they meant to do), but they'd be idiots to pull existing purchases from Amazon. Which doesn't completely disprove they wouldn't do it, but the self-interested thing to do is still to leave them on there for customers who already bought them.