User is able to move a page tree although another user is moving it at the same time

Today, I discovered that in Confluence 5.5.6 and 5.8.5 we are able to do the following:

1. User 1 moves a page tree A from space X to space Y
2. User 2 does not know that user 1 is already moving the page tree A. He is able to click on move and then moves the page tree A from space X to space Z
3. On the background, 2 requests are running trying to move page tree A to two different locations
4. After a while, user 1 will get an error 'Move failed. There was a problem contacting the server.'
5. After some time, user 2 will also get an error 'Move failed. There was a problem contacting the server.'
6. One can observer that page tree A was moved to space Z, but not completely. It seems that some pages are missing / lost.
7. User 1 and user 2 will get no notification that page tree A was moved (not completely) to space Z.

What should be done to solve this and improve page move handling?:
--> Users should not be allowed to move a page tree while another user is doing a move operation on the page tree.
---> Users should be informed properly about the ongoing process.
----> As a user I also want to see the progess (% or amount vs. total amount of pages that are moved)

From an administrator point of view, this is also annoying since it can cause deadlocks on database, higher CPU usage, ...