diff --git a/addons/mail/models/mail_composer_mixin.py b/addons/mail/models/mail_composer_mixin.py
index ddf9cf995b6..daf0aca55fd 100644
--- a/addons/mail/models/mail_composer_mixin.py
+++ b/addons/mail/models/mail_composer_mixin.py
@@ -38,18 +38,24 @@ class MailComposerMixin(models.AbstractModel):
 
     @api.depends('template_id')
     def _compute_subject(self):
+        """ Computation is coming either from template, either reset. When
+        having a template with a value set, copy it. When removing the
+        template, reset it. """
         for composer_mixin in self:
-            if composer_mixin.template_id:
+            if composer_mixin.template_id.subject:
                 composer_mixin.subject = composer_mixin.template_id.subject
-            elif not composer_mixin.subject:
+            elif not composer_mixin.template_id:
                 composer_mixin.subject = False
 
     @api.depends('template_id')
     def _compute_body(self):
+        """ Computation is coming either from template, either reset. When
+        having a template with a value set, copy it. When removing the
+        template, reset it. """
         for composer_mixin in self:
-            if composer_mixin.template_id:
+            if not tools.is_html_empty(composer_mixin.template_id.body_html):
                 composer_mixin.body = composer_mixin.template_id.body_html
-            elif not composer_mixin.body:
+            elif not composer_mixin.template_id:
                 composer_mixin.body = False
 
     @api.depends('body', 'template_id')
@@ -67,8 +73,9 @@ class MailComposerMixin(models.AbstractModel):
 
     @api.depends('template_id')
     def _compute_lang(self):
-        """ Take value form template when set. When removing the template
-        reset the value to avoid keeping part of template configuration. """
+        """ Computation is coming either from template, either reset. When
+        having a template with a value set, copy it. When removing the
+        template, reset it. """
         for composer_mixin in self:
             if composer_mixin.template_id.lang:
                 composer_mixin.lang = composer_mixin.template_id.lang
diff --git a/addons/test_mail/tests/test_mail_composer_mixin.py b/addons/test_mail/tests/test_mail_composer_mixin.py
index 24d52b076a9..b29b5a13e2a 100644
--- a/addons/test_mail/tests/test_mail_composer_mixin.py
+++ b/addons/test_mail/tests/test_mail_composer_mixin.py
@@ -79,24 +79,17 @@ class TestMailComposerMixin(TestMailCommon, TestRecipients):
 
         # template with void values: should not force void (TODO)
         composer.template_id = template_void.id
-        self.assertEqual(composer.body, f'<p><br /></p>',
-                         'TODO: should not force void value')
+        self.assertEqual(composer.body, '<p>CustomBody for <t t-out="object.name"/></p>')
         self.assertFalse(composer.body_has_template_value)
         self.assertEqual(composer.lang, template.lang)
-        self.assertEqual(composer.subject, False,
-                         'TODO: should not force void value')
-        # temporarily reput values
-        composer.body = template.body_html
-        composer.subject = template.subject
+        self.assertEqual(composer.subject, 'CustomSubject for {{ object.name }}')
 
         # reset template TOOD should reset
         composer.write({'template_id': False})
-        self.assertEqual(composer.body, self.mail_template.body_html,
-                         'TODO: should reset')
+        self.assertFalse(composer.body)
         self.assertFalse(composer.body_has_template_value)
         self.assertFalse(composer.lang)
-        self.assertEqual(composer.subject, self.mail_template.subject,
-                         'TODO: should reset')
+        self.assertFalse(composer.subject)
 
     @users("employee")
     def test_rendering_custom(self):