AP Transactions and Tax

[Peter McKenna <..hidden..>]

Hi,
I just upgraded from 1.2.9 to 1.2.16 and all seems to have gone well. Thanks to whoever did the deb package.
In 1.2.9 I began to notice the problems with AP Transactions and tax (in my case GST) not adding up properly.
I notice in 1.2.16 if I tick 'Tax Included' and the tickbox by the tax drop down but don't manually enter the tax amount tax is not calculated and posted as it should be.
If I enter the tax amount the total is wrong, it adds the tax amount to the original amount that already has tax included. That is tax is added in twice, however the figures are posted correctly in a Tax Paid report.
I've read some of the posts from Chris Travers regarding the difference in tax requirements in different parts of the world, difficulties with rounding and mixing taxable and non taxable items on the same invoice. I can appreciate that trying to have a system that is flexible enough to cover the different requirements in different countries is hard, but I would like to be able to revert my system to the way it used to work (calculate tax automatically) without reverting to an older version. 
Can someone confirm what the last release was that handled tax in the old way and ideally which code page I need to look at changing?
Regards,
Peter McKenna