(Mongo) Function MongoUpdateProperty results in unwanted side-effect

[kharybdys]

If you're using MongoUpdateProperty to update a message that represents a Mongo document in the database (eg the MatchForm collection), it results in not just updating the property but also adding an __id property if it doesn't exist yet. This property should only exist within elements of an array so it's unwanted.

First analysis is that this is due to the way MongoUpdateProperty retrieves the message(s) to change. That makes the message type "array_element" and that ensures the MessageCodec adds the __id property.

[kharybdys]

The __id property generated isn't causing any problems, it just looks odd. So urgency is low.