Order Total and Taxes inaccurate with Discount Coupon

Hi there

I'm on v1.3.8. I’ve created a discount coupon and for some reason my toatal and taxes are not properly calculated in the sequence.

Here is my coupon setup:

Coupon Name :: test
Coupon Amount :: 20.0000%
Start Date :: 03/05/2009
End Date :: 03/15/2009
Uses per Coupon :: Unlimited
Uses per Customer :: 1
Valid Product List :: --none--
Valid Categories List :: Restrictions Apply
Date Created :: 03/05/2009
Date Modified :: 03/05/2009

Coupon Zone Restriction: :: 0

This is what happens at checkout BEFORE redeeming discount coupon:

Shopping Cart Contents:

$8.80 CAD
$19.20 CAD (category allowed)
$15.00 CAD
Sub-Total: $43.00 CAD
Canada Post (1 box(es) to be shipped) (Regular, 2009-03-11): $7.70 CAD
5.0% GST XXXX + 7% PST (BC): $5.16 CAD
5% GST on shipping + 7% PST on shipping: $0.92 CAD
Total: $56.78 CAD

This is what happens at checkout AFTER redeeming discount coupon:

Sub-Total: $43.00 CAD
Canada Post (1 box(es) to be shipped) (Regular, 2009-03-11): $7.70 CAD
Discount Coupon: XXXX: -$3.84 CAD
5.0% GST XXXX + 7% PST (BC): $4.13 CAD
5% GST on shipping + 7% PST on shipping: $0.74 CAD
Total: $52.94 CAD (False)

Not only should the total substract the coupon amount but also not apply the 20% off on both taxes too.
I have 1 category restriction. The 20% off applied on 1 category only. The others one are denied.

The sort orders for all your order total modules:

Discount Coupon

This module is installed
true

Sort Order
280

Include Shipping
false

Include Tax
false

Re-calculate Tax
None

Tax Class
--none--

I have tried everything but cannot find the solution. I don't know why the discount is applied on both taxes and why the result is inaccurate. Thanks in advance for any light. Please help!!!! :lookaroun

Luna