diff --git a/addons/event/models/event_event.py b/addons/event/models/event_event.py
index ebef7dca4aa..496db204dc8 100644
--- a/addons/event/models/event_event.py
+++ b/addons/event/models/event_event.py
@@ -232,7 +232,7 @@ class EventEvent(models.Model):
             self._cr.execute(query, (tuple(self.ids),))
             res = self._cr.fetchall()
             for event_id, state, num in res:
-                results[event_id][state_field[state]] += num
+                results[event_id][state_field[state]] = num
 
         # compute seats_available
         for event in self:
diff --git a/addons/event/models/event_ticket.py b/addons/event/models/event_ticket.py
index 73a1da8f120..b4852a1e56f 100644
--- a/addons/event/models/event_ticket.py
+++ b/addons/event/models/event_ticket.py
@@ -98,6 +98,7 @@ class EventTicket(models.Model):
         for ticket in self:
             ticket.seats_unconfirmed = ticket.seats_reserved = ticket.seats_used = ticket.seats_available = 0
         # aggregate registrations by ticket and by state
+        results = {}
         if self.ids:
             state_field = {
                 'draft': 'seats_unconfirmed',
@@ -112,10 +113,11 @@ class EventTicket(models.Model):
             self.env['event.registration'].flush(['event_id', 'event_ticket_id', 'state'])
             self.env.cr.execute(query, (tuple(self.ids),))
             for event_ticket_id, state, num in self.env.cr.fetchall():
-                ticket = self.browse(event_ticket_id)
-                ticket[state_field[state]] += num
+                results.setdefault(event_ticket_id, {})[state_field[state]] = num
+
         # compute seats_available
         for ticket in self:
+            ticket.update(results.get(ticket._origin.id or ticket.id, {}))
             if ticket.seats_max > 0:
                 ticket.seats_available = ticket.seats_max - (ticket.seats_reserved + ticket.seats_used)
 
diff --git a/addons/event_sale/tests/__init__.py b/addons/event_sale/tests/__init__.py
index 47f238b93ad..0bb327b8598 100644
--- a/addons/event_sale/tests/__init__.py
+++ b/addons/event_sale/tests/__init__.py
@@ -4,3 +4,4 @@
 from . import test_event_internals
 from . import test_event_sale
 from . import test_event_sale_ui
+from . import test_event_specific
diff --git a/addons/event_sale/tests/test_event_specific.py b/addons/event_sale/tests/test_event_specific.py
new file mode 100644
index 00000000000..12c678519bb
--- /dev/null
+++ b/addons/event_sale/tests/test_event_specific.py
@@ -0,0 +1,53 @@
+# -*- coding: utf-8 -*-
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+import datetime
+
+from dateutil.relativedelta import relativedelta
+
+from odoo.addons.event_sale.tests.common import TestEventSaleCommon
+from odoo.tests.common import Form
+
+
+class TestEventSpecific(TestEventSaleCommon):
+
+    def test_event_change_max_seat_no_side_effect(self):
+        """
+        Test that changing the Maximum (seats_max), the seats_reserved of all the ticket do not change
+        """
+        # Enable "sell tickets with sales orders" so that we have a price column on the tickets
+        # Event template
+        with Form(self.env['event.type']) as event_type_form:
+            event_type_form.name = "Pastafarian Event Template"
+            # Edit the default line
+            with event_type_form.event_type_ticket_ids.new() as ticket_line:
+                ticket_line.name = 'Pastafarian Registration'
+                ticket_line.price = 0
+            event_type = event_type_form.save()
+
+        with Form(self.env['event.event']) as event_event_form:
+            event_event_form.name = 'Annual Pastafarian Reunion (APR)'
+            event_event_form.date_begin = datetime.datetime.now() + relativedelta(days=2)
+            event_event_form.date_end = datetime.datetime.now() + relativedelta(days=3)
+            event_event_form.event_type_id = event_type  # Set the template
+            event_event_form.auto_confirm = True
+            # Create second ticket (VIP)
+            with event_event_form.event_ticket_ids.new() as ticket_line:
+                ticket_line.name = 'VIP (Very Important Pastafarian)'
+                ticket_line.price = 10
+            event_event = event_event_form.save()
+
+        # Add two registrations for the event, one registration for each ticket type
+        for ticket in event_event.event_ticket_ids:
+            self.env['event.registration'].create({
+                'event_id': event_event.id,
+                'event_ticket_id': ticket.id
+            })
+
+        # Edit the maximum
+        before_confirmed = [t.seats_reserved for t in event_event.event_ticket_ids]
+        with Form(event_event) as event_event_form:
+            with event_event_form.event_ticket_ids.edit(0) as ticket_line:
+                ticket_line.seats_max = ticket_line.seats_max + 1
+        after_confirmed = [t.seats_reserved for t in event_event.event_ticket_ids]
+        self.assertEqual(before_confirmed, after_confirmed)