diff --git a/addons/sale_purchase_stock/tests/__init__.py b/addons/sale_purchase_stock/tests/__init__.py
index ec59b790bc1..54b0c0958fd 100644
--- a/addons/sale_purchase_stock/tests/__init__.py
+++ b/addons/sale_purchase_stock/tests/__init__.py
@@ -2,3 +2,4 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from . import test_sale_purchase_stock_flow
+from . import test_access_rights
diff --git a/addons/sale_purchase_stock/tests/test_access_rights.py b/addons/sale_purchase_stock/tests/test_access_rights.py
new file mode 100644
index 00000000000..fa66f4304b5
--- /dev/null
+++ b/addons/sale_purchase_stock/tests/test_access_rights.py
@@ -0,0 +1,76 @@
+# -*- coding: utf-8 -*-
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from odoo.tests import tagged
+from odoo.addons.sale_purchase.tests.common import TestCommonSalePurchaseNoChart
+
+
+@tagged('post_install', '-at_install')
+class TestAccessRights(TestCommonSalePurchaseNoChart):
+
+    @classmethod
+    def setUpClass(cls):
+        super(TestAccessRights, cls).setUpClass()
+
+        group_sale_user = cls.env.ref('sales_team.group_sale_salesman')
+
+        cls.user_salesperson = cls.env['res.users'].with_context(no_reset_password=True).create({
+            'name': 'Le Grand Jojo User',
+            'login': 'grand.jojo',
+            'email': 'grand.jojo@chansonbelge.com',
+            'groups_id': [(6, 0, [group_sale_user.id])]
+        })
+
+    def test_access_saleperson_decreases_qty(self):
+        """
+        Suppose a user who has no right on PO
+        Suppose a PO linked to a SO
+        The user decreases the qty on the SO
+        This test ensures that an activity (warning) is added to the PO
+        """
+        mto_route = self.env.ref('stock.route_warehouse0_mto')
+        buy_route = self.env.ref('purchase_stock.route_warehouse0_buy')
+        mto_route.active = True
+
+        vendor = self.env['res.partner'].create({'name': 'vendor'})
+        seller = self.env['product.supplierinfo'].create({
+            'partner_id': vendor.id,
+            'price': 8,
+        })
+
+        product = self.env['product.product'].create({
+            'name': 'SuperProduct',
+            'type': 'product',
+            'seller_ids': [(6, 0, seller.ids)],
+            'route_ids': [(6, 0, (mto_route + buy_route).ids)]
+        })
+
+        so = self.env['sale.order'].with_user(self.user_salesperson).create({
+            'partner_id': self.partner_a.id,
+            'user_id': self.user_salesperson.id,
+        })
+        so_line, _ = self.env['sale.order.line'].create([{
+            'name': product.name,
+            'product_id': product.id,
+            'product_uom_qty': 1,
+            'product_uom': product.uom_id.id,
+            'price_unit': product.list_price,
+            'tax_id': False,
+            'order_id': so.id,
+        }, {
+            'name': 'Super Section',
+            'display_type': 'line_section',
+            'order_id': so.id,
+        }])
+
+        so.action_confirm()
+
+        po = self.env['purchase.order'].search([('partner_id', '=', vendor.id)])
+        po.button_confirm()
+
+        # salesperson writes on the SO
+        so.write({
+            'order_line': [(1, so_line.id, {'product_uom_qty': 0.9})]
+        })
+
+        self.assertIn(so.name, po.activity_ids.note)
diff --git a/addons/sale_stock/models/sale_order.py b/addons/sale_stock/models/sale_order.py
index d379d865ebf..5feaa25a4ad 100644
--- a/addons/sale_stock/models/sale_order.py
+++ b/addons/sale_stock/models/sale_order.py
@@ -119,13 +119,16 @@ class SaleOrder(models.Model):
 
         res = super(SaleOrder, self).write(values)
         if values.get('order_line') and self.state == 'sale':
+            rounding = self.env['decimal.precision'].precision_get('Product Unit of Measure')
             for order in self:
                 to_log = {}
                 for order_line in order.order_line:
-                    if float_compare(order_line.product_uom_qty, pre_order_line_qty.get(order_line, 0.0), order_line.product_uom.rounding) < 0:
+                    if order_line.display_type:
+                        continue
+                    if float_compare(order_line.product_uom_qty, pre_order_line_qty.get(order_line, 0.0), precision_rounding=order_line.product_uom.rounding or rounding) < 0:
                         to_log[order_line] = (order_line.product_uom_qty, pre_order_line_qty.get(order_line, 0.0))
                 if to_log:
-                    documents = self.env['stock.picking']._log_activity_get_documents(to_log, 'move_ids', 'UP')
+                    documents = self.env['stock.picking'].sudo()._log_activity_get_documents(to_log, 'move_ids', 'UP')
                     documents = {k: v for k, v in documents.items() if k[0].state != 'cancel'}
                     order._log_decrease_ordered_quantity(documents)
         return res