I believe the OP is referring to the fact that the restore of a backup on the gateway itself does not automatically bring back the last installed security policy, and a reinstall of policy from the SMS to the gateway is necessary to get traffic flowing again. I'd say this is expected behavior, since a backup only has "configuration" data stored in it, not "state" data such as the last installed policy.
However upon revert of a snapshot on a gateway, it brings everything back including the state of the gateway's installed policy since a snapshot is essentially a full image of the system minus firewall logs.
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