Thanks Kyle.
Enabling invoicing address as non-mandatory (Paid Subscriptions | Settings | Display | Invoices) did solve the problem of the geo dependent tax showing - perhaps this should be included in the CBS documentation?
And this continued to show even after I turned the setting back to no invoicing address - in line with our test2 build.
However as soon as the tax lines showed in the basket, we were no longer able to use any promotion code. When trying to redeem a code, the page initially thought for a few seconds and then refreshed without any code showing or any error message. However it now returns the message "No unpaid payment basket found." (displayed twice with the basket no longer showing) - yet I can still see the basket in the backend.
We did have a similar problem early on with test2
www.joomlapolis.com/forum/153-professional-member-support/191725-solved-coupons-and-taxes-problem
which seemed to involve an earlier version of PHP and Zend. Both test2 and test3 are on the same server, with PHP 5.3.21 and Zend Engine 2.3.0, yet the missing promotions issue is only occurring on test3 - suggesting to me that it is due to some site/CB/CBS configuration difference. I have tried to compare screen for screen the promotion settings etc, but I think it might be something at a layer deeper than the actual promotion settings. If you agree can you help me find the bugger?