[1.8.x] Fixed #24395 -- Ensured inline ModelsForms have an updated related instance.

Backport of 4c2f546b55 from master

django/forms/models.py

@@ -891,6 +891,10 @@ class BaseInlineFormSet(BaseModelFormSet):
         return cls.fk.rel.get_accessor_name(model=cls.model).replace('+', '')
 
     def save_new(self, form, commit=True):
+        # Ensure the latest copy of the related instance is present on each
+        # form (it may have been saved after the formset was originally
+        # instantiated).
+        setattr(form.instance, self.fk.name, self.instance)
         # Use commit=False so we can assign the parent key afterwards, then
         # save the object.
         obj = form.save(commit=False)