Obsidian Depths Campaign bug

The Obsidian depths 'Archeo Gellar Field' attribute is not working as labelled. It specifically states that at level one that the system is immune to Invasions and Assaults, and of course upgrading the attribute makes the entire sector immune. However, when the Tyranid invasion event occurred a Tyranid invasion targeted the Obsidian depths immediately. This should be fixed, it is extra frustrating as in my play-through I had upgraded the system to the 3rd tier and was not expecting that system to be targeted.