This seems normal to me. In the same way that not every thing is fully inspected in normal traffic streams but goes through the fast path, ssl decryption is similarly situated. Enough needs to be seen for app-id and threat scans to do their job and the rest is fast path through. I'm not sure I follow your comment on MS ISA server. The Palo Alto is a firewall, NOT a reverse proxy. In some ways a reverse proxy is better but in other ways the Palo Alto inspections are a big improvement. If you want to reverse proxy and/or load balance the traffic you would still need another appliance to replace the ISA. This would sit behind the Palo Alto so all the inspection and firewall protection would be in place, but the traffic is buffered by the reverse proxy towards the servers.
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