You are right. This has been fixed and committed to stable repo. Thanks for reporting.

A fixed version kan be downloaded here and replaced on your server.

Joe

The 3rd arugment is 0 but it should be $supp_trans->tax_group_id. Therefore it should be look like

 $line_tax = get_full_price_for_item($entered_grn->item_code,
            $entered_grn->this_quantity_inv * $entered_grn->chg_price, $supp_trans->tax_group_id, $supp_trans->tax_included) - $taxfree_line;

Otherwise the unit_tax is not calcuated correctly because

finally the function get_tax_group_rates is not reurning the rates to calculated the full_price_of_item() on above mentioned line.