Confirm Sale and skip Payment - net_amount is getting added to prev_outstanding_balance - odoo

Question

I'm using (Bahmni with) Odoo-10 and when I press Confirm button in the Sale Order and skip/cancel the Register Payment step, the Total Outstanding amount is displayed as double the actual amount.
Here, the Previous Balance field is taking the amount in the current sale order, and then this value is also getting added with the Net Amount.
When I check the bahmni-erp/bahmni-addons/bahmni_sale/models/sale_order.py, I observe this code under SaleOrder class
prev_outstanding_balance = fields.Monetary(string="Previous Outstanding Balance",
compute=_calculate_balance)
total_outstanding_balance = fields.Monetary(string="Total Outstanding Balance",
compute=_amount_all)
def _calculate_balance(self):
for order in self:
order.prev_outstanding_balance = 0.0
order.total_outstanding_balance = 0.0
total_receivable = order._total_receivable()
order.prev_outstanding_balance = total_receivable
def _amount_all(self):
"""
Compute the total amounts of the SO.
"""
for order in self:
...
order.update({
'amount_untaxed': order.pricelist_id.currency_id.round(amount_untaxed),
'amount_tax': order.pricelist_id.currency_id.round(amount_tax),
'amount_total': amount_total + round_off_amount,
'round_off_amount': round_off_amount,
'total_outstanding_balance': order.prev_outstanding_balance + amount_total + round_off_amount
})
def _total_receivable(self):
receivable = 0.0
if self.partner_id:
self._cr.execute("""SELECT l.partner_id, at.type, SUM(l.debit-l.credit)
FROM account_move_line l
LEFT JOIN account_account a ON (l.account_id=a.id)
LEFT JOIN account_account_type at ON (a.user_type_id=at.id)
WHERE at.type IN ('receivable','payable')
AND l.partner_id = %s
AND l.full_reconcile_id IS NULL
GROUP BY l.partner_id, at.type
""", (self.partner_id.id,))
for pid, type, val in self._cr.fetchall():
if val is None:
val=0
receivable = (type == 'receivable') and val or -val
return receivable
Why it's adding the Net Amount in the current Sale Order to the prev_outstanding_balance?
Please help.
Thanks.