Maybe some commands do disable the console (maybe TGM?) but definitely not all. I've been able to get achievements just fine when I used the console a few minutes before. I've used the console to change my FOV and even once to get unstuck with TCL, and managed to get an achievement shortly after that without exiting the game.
Could be that. I'm not shy of using tgm or kill if something's becoming too tedious, as well as the subject at hand, showracemenu, since I'm perpetually unhappy with my character's appearance; I guess it's possible I've used all of them and their ilk during each session where an achievement might've been due, so it makes sense that it could be tied to specific commands. Although it's still a bit silly in a single-player game, it's less annoying if that's how they've implemented it.
Anyway, the relevance to this topic being, if anyone uses showracemenu from the command line, it's probably a good idea to save, exit and restart to avoid the risk of achievements being hampered.