I was thinking later last night and thought that might be the issue.
However, I had assumed that if the user has registered an address for his account as a billing address, and I had configured the billing address as the tax address that Hikashop might automatically look at the default billing address for the account when they login and display the prices based on that address. That seemed to me to be the most user friendly approach. That way nobody is surprised at check-out by changing prices, or turned deterred by higher prices while browsing (particularly if there are different prices in different zones).
Is that something that might be considered for a future release or are there other issues with this approach I have just not thought of yet?
thanks,