AI can build structures hidden by terrain on South Pacific map.

[pgwipeout]

I played a campaign today with three AI.
The game didn't end when I supposedly had destroyed all visible structures.
I accidentally killed a hidden structure on the northwest side of the map with a lucky weatherstorm.
The debug menu revealed the second building's location, see below at the cursor:

Also of note, both of these structures were defensive structures, which the units in the area would not auto-target with Attack-Move.

[abcdefg30]

The original had an indicator for hidden units which would solve this as well.