Don't skip Property fields in copy

trytond/model/modelstorage.py

@@ -254,7 +254,9 @@ class ModelStorage(Model):
 
                 if field_name in default:
                     data[field_name] = default[field_name]
-                elif isinstance(cls._fields[field_name], fields.Function):
+                elif (isinstance(cls._fields[field_name], fields.Function)
+                        and not isinstance(cls._fields[field_name],
+                            fields.Property)):
                     del data[field_name]
                 elif ftype in ('many2one', 'one2one'):
                     try: