Think I may have solved it.
It appears that the EasyStep form was placing my entry in one of the calculated fields instead of the correct field (in this case it was inserting it into the summation of electrical / water / gas etc field, instead of putting it into one of the GST / HST applicable or the exempt fields .
Guess I was one of the first people to use the detailed calculation via the EasySteps ;).
I ended up filling the T777s for manually instead, and that worked fine.
