I think I have figured out what is happening but don't have a solution in place at the moment. Can the people who are experiencing the issue please try the "Render Again" checkbox when editing the world and see if the new render solves the issue?
What I believe is happening is there is one server that accepts the upload and syncs that with the download server. That sync may not be happening fast enough for the render system to get the new world. So when you upload a new world it just re-renders your old world until the sync is finished. Waiting until the end of the render and rendering again should resolve it.
This may not be the problem everyone is experiencing but it's what I am seeing when I upload different versions of my test world.