Order with 2 tax rules gives negative "Total Tax" on one of them

[nfarra]

Hi, 

We have 2 tax rules in our shop: id_tax = 3 for 4% tax rate  and id_tax = 2 for 10% tax.

In orders with products associated to just on of them everything works fine. When there are products in the order with different products, in the Tax Detail box the calculations.

For proper accounting processes we need this box to show proper numbers.  I attach two examples. 

I took a look to tax tables in SQL and the look normal.. I do not have special rules or anything.

Any idea what might be triggering this behaviour? Can anybody explain where these numbers might come from?

Thanks a lot

Sample 1: Order with 1 single Tax Rate and Proper tax within "Tax Detail" box:

are wrong.

Sample 2: Order with mixed Tax Rate and strange numbers within "Tax Details" box: