I noticed this too. I think they started doing this just to make the variable more visually separated from literal strings. I don't think it makes a difference one way or another. Open one of the rules that doesn't have parenthesis, re-save the rule, and see if the parenthesis are added.
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...