[Nostalgia For Infinity]

A silly question, from a silly man!

I'm trying to change the Federation ship pictures. I go into Pictures/Races. I have no problem importing ships in from the TMP sets, but I have problems renaming some of the original ships

IE

I change the Nebula to J as a placeholder. I then try to make the Akira a heavy cruiser, but the Nebula appears in its place when I hit enter. I now have 2 Nebulas in the shipset, but no Akira!

How can I avoid this?