Coupon discount - Sub total and total calculation

[claudioerba]

Hello, I have a problem with the addon "Coupon discount" that use the GV class. I searched so many time in this forum but I don't find anything that should be useful for me. So i ask.

 

I have this problem: I set up a discount coupon with a discount of 5 euros, checkout_confirmation.php show me this:

 

discount 5

subtotal 20

tax (20%) 4

total 19

 

Opration is: (subtotal + tax [% Calculated in subtotal] ) - Discount = Total (Wrong ONE)

 

Instead this:

 

discount 5

subtotal 20

tax (20%) 3

total 18

 

Or this (is the same)

 

discount 5

subtotal 15

tax (20%) 3

total 18

 

Opration is: (subtotal - discount) + tax [% Calculated in sub - discount] = Total (Right one)

 

I tried all, change the order of the total order module, include or exclude in the options the tax calculation ... but nothing works. Where is the problem? Where can I find the file to correct?

 

Any help would be appreciated

Claudio