It might be possible.
Although unlikely. It might however be that the policy/provisioning group settings have not been upgraded properly. They should upgrade as is, but it might happen occasionally that a setting gets ' lost' .
If you fix the rights (view-only administrator, and set the rights as described in the manual), check provisioning and policies, then rerun provisioning, then sync mailboxes, you should be good to go again
Regards. Gertjan