In order to help populate a gigantic map, I created a few custom races. One of them was the "Type 14," a synthetic species with fortification as its #2 AI priority. Now this has come back to bite me as the Type 14 AI has managed to produce a planet with more than 100% defense, meaning it is completely invulnerable to ground invasion.
Here's a screenshot:
http://steamcommunity.com/sharedfiles/filedetails/?id=448815602
If I try attacking, I do no damage at all to the planet. Choosing planetary bombardment or conventional warfare makes no difference. As an aside, the invasion report will claim that I lost all 24 pop worth of attackers in the invasion, but in reality I will only lose at most one transport (= 6 pop) per attempt, so that's at least one bug.
I input the "god" command to take a look at what the AI had on this planet. Maybe it's one of those precursor shields like in the campaign?
https://steamcommunity.com/sharedfiles/filedetails/?id=448815647
No, it's just an Elerium defense shield. This looks like good use of adjacency bonuses by the AI, until you notice the Thulium archive all alone on an island.
I managed to invade the planet by destroying the shield while in god mode, but I am still wondering if this is a bug or not. Is there some way that I could have cracked this planet playing within the rules? Surely this isn't WAD?