diff --git a/addons/account/models/account_invoice.py b/addons/account/models/account_invoice.py
index 91b6d4daee8..cab5ed790f8 100644
--- a/addons/account/models/account_invoice.py
+++ b/addons/account/models/account_invoice.py
@@ -1071,6 +1071,7 @@ class AccountInvoice(models.Model):
         values['state'] = 'draft'
         values['number'] = False
         values['origin'] = invoice.number
+        values['payment_term_id'] = False
         values['refund_invoice_id'] = invoice.id
 
         if date:
@@ -1458,6 +1459,7 @@ class AccountPaymentTerm(models.Model):
     def compute(self, value, date_ref=False):
         date_ref = date_ref or fields.Date.today()
         amount = value
+        sign = value < 0 and -1 or 1
         result = []
         if self.env.context.get('currency_id'):
             currency = self.env['res.currency'].browse(self.env.context['currency_id'])
@@ -1466,7 +1468,7 @@ class AccountPaymentTerm(models.Model):
         prec = currency.decimal_places
         for line in self.line_ids:
             if line.value == 'fixed':
-                amt = round(line.value_amount, prec)
+                amt = sign * round(line.value_amount, prec)
             elif line.value == 'percent':
                 amt = round(value * (line.value_amount / 100.0), prec)
             elif line.value == 'balance':
diff --git a/addons/account/models/account_move.py b/addons/account/models/account_move.py
index 20e1c9d8886..8a28cf10b4e 100644
--- a/addons/account/models/account_move.py
+++ b/addons/account/models/account_move.py
@@ -803,7 +803,7 @@ class AccountMoveLine(models.Model):
         elif self._context.get('skip_full_reconcile_check') == 'amount_currency_only':
             field = 'amount_residual_currency'
         #target the pair of move in self that are the oldest
-        sorted_moves = sorted(self, key=lambda a: a.date)
+        sorted_moves = sorted(self, key=lambda a: a.date_maturity or a.date)
         debit = credit = False
         for aml in sorted_moves:
             if credit and debit: