Sales Tax & Discount Coupon problems

Ive been trying for hours to figure this out but i cannot get discount coupons and taxes to work together. So now the basics, i have zen 1.3.7 and here is the order totals:

Sub-Total: $213.37
Group Discount: $0.00
Free Shipping Options (Free Shipping): $0.00
Discount Coupon: 03560 : -$21.34
15% HST: $16.01
Total: $208.04

Now obviously this doesnt add up. The coupon is for 10% off, the tax is based soley on the new subtotal after the discount. So the numbers should be:

Sub-Total: $213.37
Group Discount: $0.00
Free Shipping Options (Free Shipping): $0.00
Discount Coupon: 03560 : -$21.34
15% HST: $28.80
Total: $220.83

Without a discount the tax works just fine. Now for my order total settings:

ot_coupon is on, sort is 280, include shipping is false, include tax is false, re-calc tax is standard, tax class is none.

ot_tax is on, sort order is 300

No matter how i change the ot_coupon settings it either charges tax based on the full order subtotal before the discount or this odd number above, which makes no sense at all.

Any help would be great

Any help on this?

What if you put the value "include tax is true" ?

let say now you have 10% reduction on your item: x - 0.1x = 0.9x
add tax: 0.9x + 0.135x = 1.035x

if you include tax :

you would have x + 0.15x = 1.15x
reduction10% : 1.15x - 0.115x = 1.035x

same result i would say

I have a simular problem with group-discount. For me its just the other way around.

i use a group discount of 10% and with tax = true i get
for 3 items i get following invoice

Tax items Price (ex) Price (inc) Total (ex) Total (inc)

6% 2x €11,250.00 €11,925.00 €22,500.00 €23,850.00
6% x €11,450.00 €12,137.00 €11,450.00 €12,137.00
Sub-Total: 35,987.00 (tax incl) shipping: €8.50
Group Discount: -€3,802.40
tax : €1,833.30
Total: €32,193.10

No idea how i can give 3,802 for discount

Ive changed every combination of settings under ot_tax and discount to try and solve it with no solution. Also now when tax and a discount coupon are used, its placing the order as gift certificate/coupon and not charging the credit card.

there is an other treath about this problem as well, i found now, http://www.zen-cart.com/forum/showthread.php?t=124685&highlight=discount+calculation

Not sure if its of any help.