# -*- coding: utf-8 -*-
# © 2016 Carlos Dauden <carlos.dauden@tecnativa.com>
# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).

from openerp import api, models


class PurchaseOrderLine(models.Model):
    _inherit = 'account.analytic.account'

    @api.multi
    def _recurring_create_invoice(self, automatic=False):
        invoice_obj = self.env['account.invoice']
        invoices = invoice_obj.browse(
            super(PurchaseOrderLine, self)._recurring_create_invoice(
                automatic))
        res = []
        unlink_list = []
        for partner in invoices.mapped('partner_id'):
            inv_to_merge = invoices.filtered(
                lambda x: x.partner_id.id == partner)
            if partner.contract_invoice_merge and len(inv_to_merge) > 1:
                invoices_merged = inv_to_merge.do_merge()
                res.extend(invoices_merged)
                unlink_list.extend(inv_to_merge)
            else:
                res.extend(inv_to_merge)
        if unlink_list:
            invoice_obj.browse(unlink_list).unlink()
        return res

# -*- coding: utf-8 -*-
# © 2016 Carlos Dauden <carlos.dauden@tecnativa.com>
# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).

from openerp import api, models


class PurchaseOrderLine(models.Model):
    _inherit = 'account.analytic.account'

    @api.multi
    def _recurring_create_invoice(self, automatic=False):
        invoice_obj = self.env['account.invoice']
        invoices = invoice_obj.browse(
            super(PurchaseOrderLine, self)._recurring_create_invoice(automatic))
        res = []
        unlink_list = []
        for partner in invoices.mapped('partner_id'):
            inv_to_merge = invoices.filtered(
                lambda x: x.partner_id.id == partner)
            if partner.contract_invoice_merge:
                invoices_merged = inv_to_merge.do_merge()
                res.extend(invoices_merged)
                unlink_list.extend(inv_to_merge)
            else:
                res.extend(inv_to_merge)
        if unlink_list:
            invoice_obj.unlink([x.id for x in unlink_list])
        return res

--- 
+++ 
@@ -12,18 +12,19 @@
     def _recurring_create_invoice(self, automatic=False):
         invoice_obj = self.env['account.invoice']
         invoices = invoice_obj.browse(
-            super(PurchaseOrderLine, self)._recurring_create_invoice(automatic))
+            super(PurchaseOrderLine, self)._recurring_create_invoice(
+                automatic))
         res = []
         unlink_list = []
         for partner in invoices.mapped('partner_id'):
             inv_to_merge = invoices.filtered(
                 lambda x: x.partner_id.id == partner)
-            if partner.contract_invoice_merge:
+            if partner.contract_invoice_merge and len(inv_to_merge) > 1:
                 invoices_merged = inv_to_merge.do_merge()
                 res.extend(invoices_merged)
                 unlink_list.extend(inv_to_merge)
             else:
                 res.extend(inv_to_merge)
         if unlink_list:
-            invoice_obj.unlink([x.id for x in unlink_list])
+            invoice_obj.browse(unlink_list).unlink()
         return res
Fix unlink, >1 filter and lines too long