I have also seen this before. I will need to double check in the lab but I dont think the counter will increment because there is not any aaa seesion id to track that session with. Also with the service type set to login that might be why the counter may not increment.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...