Yeah, I came to the same conclusion. I didn't want to go mucking around in the jQuery source changing core functionality, so I managed a work around by copying the data into an interim object, setting flags in the container to know when an item has been received and when to copy data, etc. Total hack, in other words. ;P
It is absolutely inexplicable to me that at no time is the old item (ui.sender in this case) visible to the new ui.item; Especially in the event in which it is likely you'll need to be able to do exactly that. Furthermore, I'm puzzled as to why, in that very event, ui.sender and ui.item references to the same object...
Oh well. Despite this little hiccup, I've really enjoyed using jQuery for this project.