How do you stop folders from being deleted in your archive?

This is a niggling bug that is driving one of our customers crazy. They archive mail to a server based archive and this mail is in folders (several levels deep). Works well. But when they delete an empty folder from their mail file, the folder in the archive is also deleted. How do you 'turn this feature off'. We have tried changing the replication settings on the archive to not replicate deletions but that does not work.