Ok, that was a bad idea.

InvenTree/InvenTree/serializers.py

@@ -50,7 +50,6 @@ class InvenTreeModelSerializer(serializers.ModelSerializer):
 
         # Now ensure the underlying model is correct
         instance = self.Meta.model(**data)
-        instance.validate_unique()
         instance.clean()
 
         return data

InvenTree/part/models.py

@@ -380,7 +380,6 @@ class Part(MPTTModel):
                     previous.image.delete(save=False)
 
         self.clean()
-        self.validate_unique()
 
         super().save(*args, **kwargs)
 
@@ -672,6 +671,8 @@ class Part(MPTTModel):
 
         super().clean()
 
+        self.validate_unique()
+
         if self.trackable:
             for part in self.get_used_in().all():