i;ve been pulling my hair lately over the group discount and tax problem as identified here

zencart 1.3.8
mysql 5.0.45
apache 2.2.6
php 5.2.5
installed module: Euro VAT 1.3.0

Here are my settings for GroupDiscount in Order Total Modules

This module is installed: true
Sort Order: 120
Include Shipping value in amount before discount calculation? false
Include Tax: false
Re-calculate Tax: Standard
Tax Class: None
discount: 50%
(i've also tried with Re-calculate tax: none with same result)

my sort order:
sub total: 100
group discount: 120
shipping: 200
tax: 800
total: 999

here is a sample example of incorrectly calculated tax and as a result total:

Sub-Total: €1,800.00
Group Discount: -€900.00
UPS (Air Express Shipping (2-4 days)): €21.00
VAT 22% EU: €200.31
Total: €1,121.31

VAT should be 202.62
Total should be: 1102.62

It looks like, to me, that tax is being computed based on the full amount (subtotal+ship) then discounted by the group discount ((1800+21) x .22) x .5 = 200.31

how do i set it up so that the discount does not include the shipping and tax... (notice include tax and include ship are off above)

((1800x.5)+21) x .22 = 202.62

thanks for the help here are some images :)

sort order


sample incorrect output