In a number of my TA games, I've noticed that the AI Terrans and/or Drengin seem to be suffering from some kind of ship-building bug where their Defenders use a random medium-hull template for their appearance instead of the normal Terran or Drengin defender template. On a few occasions, I've even seen the Terrans use custom medium hulls that I had saved earlier for their defenders. This only seems to occur when I'm playing with mods enabled, but I don't actually have any mods that would cause this. This only seems to happen with the Terrans and Drengin; other races, even other races using the Terran or Drengin ship styles, seem unaffected.
The change is purely in appearance - the defender is still treated as having a small hull - but it looks bizarre.