List item system_update does not update item

[daarsan]

Hi all, I've been doing some stuff with SharePoint lists and items, but unfortunately I am facing an issue that can be solved through a workaround. However I was wondering if there is a better way. To simplify the scenario, I would summarize this question to:

1. We have an item that needs to update a column (ideally a column starting with underscore i.e. __test that is transformed into OData___test, but for the sake of this test we can assume it is called "test").
2. The update cannot modify version history, editor, modification date, etc. ONLY the mentioned column.
3. The column should be a datetime column but we can assume it is a text property.
4. I'm using version is 2.5.9.

My code is:

sp_item = self.list.items.get_by_id(id)
property_name = "test"
property_value = "whatever"
sp_item = sp_item.set_property(property_name, property_value).system_update()
sp_item.context.load(sp_item)
sp_item.context.execute_query()

The expected result is to have sp_item.get_property(property_name) equal to property_value, but it is None. Any idea why this is not working as expected? I was looking at the samples, but this method does not have too much information.

PS: My workaround is to use validate_update_list_item overriding Modified and Editor with the current values, but I was wondering why system_update does not update the item.