v. 1.9
If I have two ground units with either Ground Survey or Xeno Archaeology equipment, but they are still slightly different, and I obsolete one of them, they are both obsoleted. I have experienced the same thing in an earlier version and now as well in my 1.9 game. I have been unable to reproduce the bug in a different game - partly because I am not sure what conditions cause, so I have instead attached by DB.