diff --git a/__manifest__.py b/__manifest__.py
index 9d4ee19..5e4c2c7 100644
--- a/__manifest__.py
+++ b/__manifest__.py
@@ -18,7 +18,7 @@
 #
 {
     'name': 'bemade_multiple_billing_contacts',
-    'version': '15.0.1.0.0',
+    'version': '15.0.1.0.1',
     'summary': 'Send invoices to multiple contacts by default.',
     'description': """By default, newly created invoices add all invoice addresses for the given partner as
                       followers on the invoice. If billing contacts are set manually on the sales order, those billing
diff --git a/models/account_move.py b/models/account_move.py
index e5b191a..a12ddda 100644
--- a/models/account_move.py
+++ b/models/account_move.py
@@ -25,8 +25,8 @@ class AccountMove(models.Model):
     def _post(self, soft=True):
         # Override the original method to subscribe the partner's billing contacts instead of self.partner_id
         initial_subscribers = self.message_partner_ids.ids
-        final_subscribers = initial_subscribers + self.partner_id.billing_contacts.ids
+        final_subscribers = initial_subscribers + self.billing_contacts.ids
         posted = super()._post()
-        self.message_unsubscribe(self.message_partner_ids - initial_subscribers)
+        self.message_unsubscribe([s.id for s in self.message_partner_ids if s not in initial_subscribers])
         self.message_subscribe(final_subscribers)
         return posted
diff --git a/tests/test_billing_contacts.py b/tests/test_billing_contacts.py
index 47f0a9b..c99d4d5 100644
--- a/tests/test_billing_contacts.py
+++ b/tests/test_billing_contacts.py
@@ -1,6 +1,9 @@
 from odoo.tests import TransactionCase, tagged
+from odoo import Command
+import datetime
 
 
+@tagged('-at_install', 'post_install')
 class TestBillingContacts(TransactionCase):
     @classmethod
     def setUpClass(cls):
@@ -31,10 +34,74 @@ class TestBillingContacts(TransactionCase):
             'parent_id': cls.parent_co.id,
             'type': 'contact',
         })
+        cls.product = cls.env['product.product'].with_company(cls.parent_co.company_id).create({
+            'name': 'Product',
+            'categ_id': cls.env['product.category'].create({'name': 'Product Category'}).id,
+            'list_price': 100.0,
+            'type': 'service',
+            'uom_id': cls.env.ref('uom.product_uom_unit').id,
+            'uom_po_id': cls.env.ref('uom.product_uom_unit').id,
+            'default_code': 'PRODUCT-X',
+            'invoice_policy': 'order',
+            'expense_policy': 'no',
+            'taxes_id': [(6, 0, [])],
+            'supplier_taxes_id': [(6, 0, [])],
+        })
 
-    @tagged('-at_install', 'post_install')
-    def test_sale_order_defaults(self):
-        billing_contacts = self.parent_co.billing_contacts
+        cls.sale_order = cls.env['sale.order'].create({
+            'partner_id': cls.parent_co.id,
+            'client_order_ref': 'abc123',
+        })
+
+        cls.env['sale.order.line'].create({
+            'product_id': cls.product.id,
+            'name': cls.product.name,
+            'product_uom_qty': 2,
+            'product_uom': cls.product.uom_id.id,
+            'price_unit': cls.product.list_price,
+            'order_id': cls.sale_order.id,
+            'tax_id': False,
+            'qty_delivered_manual': 2,
+        })
+
+    def test_billing_contacts_structure(self):
         self.assertTrue(self.billing_contact1 in self.parent_co.billing_contacts)
         self.assertTrue(self.billing_contact2 in self.parent_co.billing_contacts)
         self.assertTrue(self.non_billing_contact not in self.parent_co.billing_contacts)
+
+    def test_sale_order_default_billing_contacts(self):
+        self.assertTrue(self.sale_order.billing_contacts == self.parent_co.billing_contacts)
+
+    def test_sale_order_change_contacts(self):
+        # Test that changing the billing contacts on an SO doesn't change them on the partner
+        # Validate that changing them manually on the SO transfers to the invoice
+        self.sale_order.write({'billing_contacts': [Command.link(self.non_billing_contact.id)]})
+        self.assertTrue(all([c in self.sale_order.billing_contacts for c in self.parent_co.billing_contacts]))
+        self.assertTrue(self.non_billing_contact not in self.parent_co.billing_contacts)
+        self.assertTrue(self.non_billing_contact in self.sale_order.billing_contacts)
+
+    def test_sale_order_to_invoice_contacts(self):
+        # Test that the invoices created from sales orders take the billing contacts configured on the SO
+
+        self.sale_order.write({'billing_contacts': [Command.link(self.non_billing_contact.id)]})
+        self.sale_order.action_confirm()
+
+        wiz = self.env['sale.advance.payment.inv'].create({})
+        invoice = wiz._create_invoice(self.sale_order,self.sale_order.order_line[0],self.sale_order.order_line.price_total)
+        self.assertTrue(invoice)
+        self.assertTrue(invoice.billing_contacts == self.sale_order.billing_contacts)
+
+    def test_direct_invoice_contacts(self):
+        invoice = self.env['account.move'].create({
+            'move_type': 'out_invoice',
+            'partner_id': self.parent_co,
+        })
+        self.assertTrue(self.parent_co.billing_contacts == invoice.billing_contacts)
+
+    def test_invoice_followers_on_validate(self):
+        self.sale_order.action_confirm()
+        wiz = self.env['sale.advance.payment.inv'].create({})
+        invoice = wiz._create_invoice(self.sale_order,self.sale_order.order_line[0],self.sale_order.order_line.price_total)
+        invoice.write({'date': datetime.date.today()})
+        invoice.action_post()
+        self.assertTrue(all([r in invoice.message_partner_ids for r in self.parent_co.billing_contacts]))