Price without VAT calculation not correct!

I love the invoice module, but when testing it before going live, I found a bug in the code.
When you add an item to the invoice, that has a VAT percentage that differs from the standerd VAT percentage, the Price without VAT is not correctly calculated.
(when you fill out the Price incl. VAT)

the code uses the standard VAT percentage, and not the percentage that is added to the item information.
to correct this you simply need to change the code in the invoice.ajax.inc file, line 178 as follows.

this uses the form VAT amount and not the standard VAT amount.

I hope this helps others. and improve this module in the future.

$unitcost = $fv['price_with_vat'] / _invoice_vat_percent_to_decimal($fv['vat']);