I found this bug 2 years ago but I cannot find the cause. Just today that I tried to fix it again and found that the SQL in report709.php seems to be unreasonable as the following.
$sql = "SELECT tt.name as taxname, taxrec.*, taxrec.amount*ex_rate AS amount,
taxrec.net_amount*ex_rate AS net_amount,
IF(taxrec.trans_type=".ST_BANKPAYMENT." OR taxrec.trans_type=".ST_BANKDEPOSIT.",
IF(gl.person_type_id<>".PT_MISC.", gl.memo_, gl.person_id),
IF(ISNULL(supp.supp_name), debt.name, supp.supp_name)) as name,
FROM ".TB_PREF."trans_tax_details taxrec
LEFT JOIN ".TB_PREF."tax_types tt
LEFT JOIN ".TB_PREF."gl_trans gl
ON taxrec.trans_type=gl.type AND taxrec.trans_no=gl.type_no AND
(tt.purchasing_gl_code=gl.account OR tt.sales_gl_code=gl.account)
LEFT JOIN ".TB_PREF."supp_trans strans
ON taxrec.trans_no=strans.trans_no AND taxrec.trans_type=strans.type
LEFT JOIN ".TB_PREF."suppliers as supp ON strans.supplier_id=supp.supplier_id
LEFT JOIN ".TB_PREF."debtor_trans dtrans
ON taxrec.trans_no=dtrans.trans_no AND taxrec.trans_type=dtrans.type
LEFT JOIN ".TB_PREF."debtors_master as debt ON dtrans.debtor_no=debt.debtor_no
LEFT JOIN ".TB_PREF."cust_branch as branch ON dtrans.branch_code=branch.branch_code
WHERE (taxrec.amount <> 0 OR taxrec.net_amount <> 0)
AND taxrec.trans_type <> ".ST_CUSTDELIVERY."
AND taxrec.tran_date >= '$fromdate'
AND taxrec.tran_date <= '$todate'
ORDER BY taxrec.trans_type, taxrec.tran_date, taxrec.trans_no, taxrec.ex_rate";
When there are 2 records in tax_trans (The amount value in one record is not 0 and the other one is 0) which linked to the same record in debtor_trans, this SQL will generate 2 records after joining.
In tax_trans, the record of amount value 0 is filtered out by WHERE parameters, and only 1 tax_tran will be activated to join. But in joining gl_trans, the record of amount 0 is not filtered out so they all will be joined with this 1 tax_tran and get 2 transactions in the report.
Just add " AND (gl.amount <> 0)" into the LEFT JOIN of gl_trans. This is what I have done so far. However, I do not really know the side effect as I have never thoroughly get into the codes of FrontAccounting.