Is it a bug?
It's irritating seeing the achievement icon turn green (indicating earning a new achievement) only to see this stale thing over and over again.
This is not a bug.
This badge is awarded per site, so when you join 10 sites, you will get 10 badges since the About Me is being copied upon account association. As you can see to the left of the badge icon, that one was for Movies.SE site you joined today.
However, once you get 200 reputation on one site, you are considered a "veteran user", and you'll stop being notified about "trivial" badges like this one. (You will still get them, just without notification in your inbox.)