[ic] SalexTax multi error with discount products

[interchange-users@icdevgroup.org]

There is an error in [salestax] calculation with [discount] products, the 
tax is calculated with the regular price, instead subtotal

It works OK with default salestax configuration, but fail with 
VAT, based on country and tax category. (SalexTax multi)

My catalog.cfg :

#SalesTax        __TAXFIELD__
SalesTax        multi
TaxShipping     __TAXSHIPPING__


example:

105.26 less 5% discount = 100 + 16%  (16.00) = 116.00

but the interchange calculation is:

105.26 less 5% discount = 100 + 16% (16.84) = 116.84

Salestax was 16.84  instead the correct valor 16.00

Version 4.9.3 
Tax configuration:
Tax type :VAT, based on country and tax category


Tested also with 4.8.6 (same problem)

best regards
Salvador Caballe