I think the issue that you see here is because of two reasons -
a) the mapped IP in your case is the outside interface IP address and in this scenario you would expect to see the traffic getting dropped with the syslog message you mentioned.
b) the source for this traffic should also be NAT'ed so that the reply packets from the internal server make its way back through the firewall. --> this however, is only a secondary issue and can be corrected using NAT.
Now, let us consider that you are using a different IP address from the interface IP on the outside to NAT the internal server. In that case, following is the NAT that needs to be configured on the ASA -
I think there is some confusion on what you think DNS doctoring is doing.
Its nothing to do with different ports or services, it changes the embedded IP address with in a DNS response so that a client can successfully connect to the correct IP address of a server that lies internally
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...