diff --git a/addons/event/models/event_registration.py b/addons/event/models/event_registration.py
index b9d88dab020..e22283172e2 100644
--- a/addons/event/models/event_registration.py
+++ b/addons/event/models/event_registration.py
@@ -31,10 +31,10 @@ class EventRegistration(models.Model):
         states={'done': [('readonly', True)]})
     name = fields.Char(
         string='Attendee Name', index=True,
-        compute='_compute_contact_info', copy=True, readonly=False, store=True, tracking=True)
-    email = fields.Char(string='Email', compute='_compute_contact_info', copy=True, readonly=False, store=True)
-    phone = fields.Char(string='Phone', compute='_compute_contact_info', copy=True, readonly=False, store=True)
-    mobile = fields.Char(string='Mobile', compute='_compute_contact_info', copy=True, readonly=False, store=True)
+        compute='_compute_contact_info', copy=True, readonly=False, store=True, tracking=10)
+    email = fields.Char(string='Email', compute='_compute_contact_info', copy=True, readonly=False, store=True, tracking=11)
+    phone = fields.Char(string='Phone', compute='_compute_contact_info', copy=True, readonly=False, store=True, tracking=12)
+    mobile = fields.Char(string='Mobile', compute='_compute_contact_info', copy=True, readonly=False, store=True, tracking=13)
     # organization
     date_open = fields.Datetime(string='Registration Date', readonly=True, default=lambda self: fields.Datetime.now())  # weird crash is directly now
     date_closed = fields.Datetime(
@@ -50,6 +50,26 @@ class EventRegistration(models.Model):
         ('open', 'Confirmed'), ('done', 'Attended')],
         string='Status', default='draft', readonly=True, copy=False, tracking=True)
 
+    @api.onchange('partner_id')
+    def _onchange_partner_id(self):
+        """ Keep an explicit onchange on partner_id. Rationale : if user explicitly
+        changes the partner in interface, he want to update the whole customer
+        information. If partner_id is updated in code (e.g. updating your personal
+        information after having registered in website_event_sale) fields with a
+        value should not be reset as we don't know which one is the right one.
+
+        In other words
+          * computed fields based on partner_id should only update missing
+            information. Indeed automated code cannot decide which information
+            is more accurate;
+          * interface should allow to update all customer related information
+            at once. We consider event users really want to update all fields
+            related to the partner;
+        """
+        for registration in self:
+            if registration.partner_id:
+                registration.update(registration._synchronize_partner_values(registration.partner_id))
+
     @api.depends('partner_id')
     def _compute_contact_info(self):
         for registration in self:
diff --git a/addons/event/tests/test_event_flow.py b/addons/event/tests/test_event_flow.py
index 1ec9208e1b3..ff114bb4196 100644
--- a/addons/event/tests/test_event_flow.py
+++ b/addons/event/tests/test_event_flow.py
@@ -7,9 +7,69 @@ from dateutil.relativedelta import relativedelta
 
 from odoo.addons.event.tests.common import TestEventCommon
 from odoo.exceptions import ValidationError
+from odoo.tests.common import Form
 from odoo.tools import mute_logger
 
 
+class TestEventUI(TestEventCommon):
+
+    def test_event_registration_partner_sync(self):
+        """ Ensure onchange on partner_id is kept for interface, not for computed
+        fields. """
+        registration_form = Form(self.env['event.registration'].with_context(
+            default_name='WrongName',
+            default_event_id=self.event_0.id
+        ))
+        self.assertEqual(registration_form.event_id, self.event_0)
+        self.assertEqual(registration_form.name, 'WrongName')
+        self.assertFalse(registration_form.email)
+        self.assertFalse(registration_form.phone)
+        self.assertFalse(registration_form.mobile)
+
+        # trigger onchange
+        registration_form.partner_id = self.customer
+        self.assertEqual(registration_form.name, self.customer.name)
+        self.assertEqual(registration_form.email, self.customer.email)
+        self.assertEqual(registration_form.phone, self.customer.phone)
+        self.assertEqual(registration_form.mobile, self.customer.mobile)
+
+        # save, check record matches Form values
+        registration = registration_form.save()
+        self.assertEqual(registration.partner_id, self.customer)
+        self.assertEqual(registration.name, self.customer.name)
+        self.assertEqual(registration.email, self.customer.email)
+        self.assertEqual(registration.phone, self.customer.phone)
+        self.assertEqual(registration.mobile, self.customer.mobile)
+
+        # allow writing on some fields independently from customer config
+        registration.write({'phone': False, 'mobile': False})
+        self.assertFalse(registration.phone)
+        self.assertFalse(registration.mobile)
+
+        # reset partner should not reset other fields
+        registration.write({'partner_id': False})
+        self.assertEqual(registration.partner_id, self.env['res.partner'])
+        self.assertEqual(registration.name, self.customer.name)
+        self.assertEqual(registration.email, self.customer.email)
+        self.assertFalse(registration.phone)
+        self.assertFalse(registration.mobile)
+
+        # update to a new partner not through UI -> update only void feilds
+        customer2 = self.env['res.partner'].create({
+            'name': 'Constantin Customer 2',
+            'email': 'constantin2@test.example.com',
+            'country_id': self.env.ref('base.be').id,
+            'phone': '0456987654',
+            'mobile': '0456654321',
+        })
+        registration.write({'partner_id': customer2.id})
+        self.assertEqual(registration.partner_id, customer2)
+        self.assertEqual(registration.name, self.customer.name)
+        self.assertEqual(registration.email, self.customer.email)
+        self.assertEqual(registration.phone, customer2.phone)
+        self.assertEqual(registration.mobile, customer2.mobile)
+
+
 class TestEventFlow(TestEventCommon):
 
     @mute_logger('odoo.addons.base.models.ir_model', 'odoo.models')