Image files deleted from server

Server: Windows Server 2008 Standard
Client: Acronis True Image Home 2012 Plus Pack, Update 2.1 (build 7133)
PC OS: Windows 7 SP1 Enterprise

We are running TIH2012 on 4 PCs. We are creating images manually from various production PCs, using CDs, USB flash drives and USB HDDs. These images are then copied to a folder on a file server for storage. This folder has only two NTFS permissions as follows. The local Everyone account has Read & Execute permission, and a domain account, SmithJohn, has full control. Inheritable parent permissions is turned off. The owner is DOMAIN\SmithJohn. It is not directly shared, it is inside a shared folder. The local Everyone account, the local Administrators group and the DOMAIN\DomainAdmins group all have Full Control share permissions.

The server has Acronis Backup & Recovery 10 installed. The following service are running there: Acronis Managed Machine Service, Acronis Remote Agent Service, Acronis Scheduler 2 Service, Acronis VSS Provider, Backup Exec Error Recording Service, Backup Exec PureDisk Filesystem Service and Backup Exec Remote Agent for Windows Systems.

Occasionally a member of DOMAIN\DomainAdmins will browse for backups, connecting to an image on this server. If he then right-clicks that backup and chooses Delete, the image is deleted from the server. The permissions seem to make that impossible. This archive contains our gold images and are not to be deleted, except by DOMAIN\SmithJohn.

What am I missing?