Coupons and Tax calculation in Europe

Hello,

First of all my best wishes for year 2008 to all ZenCart Team that participate to the success of ZC. And also all of you who read this post.

I spent a billion hours trying to corectly set the ot_coupon module without success!
The problem is that either redemption is good and tax false or redemption is false et tax good.

Can you help me to set correctly this module. Hereafter is the result I want to obtain :

• Price of the product including VAT : 100 euros
• Rebate to apply on price above : 10%
• Calculated Rebate amount : -10 euros

• Price to pay including VAT : 90 euros

• VAT (for example): 20%

• VAT amount calculated and display on invoice : 15 euros
  

I test I think all the options of the module and never achieve to get this result.

I think it could be a bug of ZC1.3.7!? If yes, is it corrected in 1.3.8?

Thanks in advance for your answers.