Assigning one book per block and locking it there

Hi,
I asked a while ago on this topic. I want to assign exactly one book per block but when a page in another book is edited it tends to add that book to every block. Is there a way to turn off this behaviour? I was advised before that an upcoming version would allow us to lock the blocks. At the moment I have to periodically uncheck out of place books in every block after an editor makes changes to a page.