Fix a severe bug in VariationField

src/pretix/base/models.py

@@ -649,12 +649,12 @@ class PropertyValue(Versionable):
         if self.prop:
             self.prop.event.get_cache().clear()
 
+    @property
+    def sortkey(self):
+        return self.position, self.pk
+
     def __lt__(self, other):
-        if self.position < other.position:
-            return True
-        if self.position == other.position:
-            return self.pk < other.pk
-        return False
+        return self.sortkey < other.sortkey
 
 
 class Question(Versionable):

src/pretix/control/views/forms.py

@@ -179,7 +179,7 @@ class VariationsFieldRenderer(forms.widgets.CheckboxFieldRenderer):
             def sort(v):
                 # Given a list of variations, this will sort them by their position
                 # on the x-axis
-                return v[prop2.identity].identity
+                return v[prop2.identity].sortkey
 
             # We now iterate over the cartesian product of all the other
             # properties which are NOT on the axes of the grid because we

src/pretix/control/views/item.py

@@ -765,7 +765,7 @@ class ItemVariations(ItemDetailMixin, EventPermissionRequiredMixin, TemplateView
             def sort(v):
                 # Given a list of variations, this will sort them by their position
                 # on the x-axis
-                return v[prop2.identity].identity
+                return v[prop2.identity].sortkey
 
             # We now iterate over the cartesian product of all the other
             # properties which are NOT on the axes of the grid because we