@evansnp If the SH2 worked as who intended? We all think we know what it should do, but it could well be that someone in the BT team has other ideas for reasons unknown to the rest of the world!
At least you have a working solution, you could always introduce your own router just acting as a switch, DHCP server, and WAP leaving the SH2 for simple routing and DV.
I have never played with a Mikrotik but thought you could use it as a firewall in bridge mode rather than router mode. I may be completely wrong by the way because as I said I have never had a chance to play with one.