I took over a planet with a fleet of transports, it gave me an insane population and an insane influence. It went back to normal after 2 turns. I got a screen shot, so here you go:
http://img161.imageshack.us/img161/5620/wow7qd.jpg
Now that I think about it, it probably went back to normal because everyone starved to death. It didn't happen when I invaded any other planets, but I think that was one of the few that I invaded with a fleet of transports, rather than 1 at a time.
