always copy dict on Location.__init__ because it could be the default

src/c3nav/mapdata/models/locations.py

@@ -57,6 +57,10 @@ class Location(LocationSlug, EditorFormMixin, models.Model):
     class Meta:
         abstract = True
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.titles = self.titles.copy()
+
     def serialize(self, detailed=True, **kwargs):
         result = super().serialize(**kwargs)
         if not detailed: