I haven't deleted any units or their portraits between patches, so I don't know if that is causing the problem. The units all start out with the correct portrait, then they get messed up. Some portraits are missing, then they reappear, but usually not. Some are mixed up with champion's portraits. Here is a chronological series of portrait mixups.
edit - Debug and autosave files in zip -
http://dl.dropbox.com/u/16872572/nportraits.zip
No portrait for the forward observer.
A little later, no portrait for the forward observer or guardian.
Later, the guardian has his portrait but the Kings Ward adopted a champion's portrait. Forward Observer still missing portrait.
A little later in the game, the Baron lost his portrait. I don't have a good picture of that but you can see the black box in my other thread about ZOC.
