Avoid issues with duplicate ItemBundles

src/pretix/base/services/orders.py

@@ -553,6 +553,8 @@ def _check_positions(event: Event, now_dt: datetime, positions: List[CartPositio
                 bprice = bundle.designated_price or 0
             except ItemBundle.DoesNotExist:
                 bprice = cp.price
+            except ItemBundle.MultipleObjectsReturned:
+                raise OrderError("Invalid product configuration (duplicate bundle)")
             price = get_price(cp.item, cp.variation, cp.voucher, bprice, cp.subevent, custom_price_is_net=False,
                               invoice_address=address, force_custom_price=True, max_discount=max_discount)
             pbv = get_price(cp.item, cp.variation, None, bprice, cp.subevent, custom_price_is_net=False,

src/pretix/control/forms/item.py

@@ -684,6 +684,27 @@ class ItemBundleFormSet(I18nFormSet):
         self.add_fields(form, None)
         return form
 
+    def clean(self):
+        super().clean()
+        ivs = set()
+        for i in range(0, self.total_form_count()):
+            form = self.forms[i]
+            if self.can_delete:
+                if self._should_delete_form(form):
+                    # This form is going to be deleted so any of its errors
+                    # should not cause the entire formset to be invalid.
+                    try:
+                        ivs.remove(form.cleaned_data['itemvar'])
+                    except KeyError:
+                        pass
+                    continue
+
+            if 'itemvar' in form.cleaned_data:
+                if form.cleaned_data['itemvar'] in ivs:
+                    raise ValidationError(_('You added the same bundled product twice'))
+
+                ivs.add(form.cleaned_data['itemvar'])
+
 
 class ItemBundleForm(I18nModelForm):
     itemvar = forms.ChoiceField(label=_('Bundled product'))