Directory and Resource Administrator 6.x
Directory and Resource Administrator 7.x
Assistant Admins are able to change the mailbox store location when cloning an account via the MMC.
This is the correct behavior.
A pre-task trigger can be used to limit where the mailbox is created. A pretask trigger is available on the Knowledge Depot and the trigger is called CreateMailbox.vbs. This pretask trigger creates a mailbox on a specific mailboxstore specified in the script when creating a new user. This trigger should be tied to the UserCreate and UserCopy operation. The script will require modification of the LDAP path to the mailbox store where the mailbox will be created.
The script is available on the Knowledge Depot at https://www.netiq.com/support/dra/extended/knowledgedepot/default.asp
This script could be modified to take the mailbox store of the template account and use this mailboxstore for the cloned account.