Usernames ending in "json" cause trouble

Question

When you visit a user's profile page, the actual username in the URL isn't supposed to matter. For example, all these URLs go to the same place:
https://stackoverflow.com/users/1/jeff-atwood
https://stackoverflow.com/users/1/jeff-the-dragon
https://stackoverflow.com/users/1

However, if your username happens to end in the letters json, your profile page gets screwed up:
https://stackoverflow.com/users/1/jeffendinginjson

Answer 1

I'm sorry, I won't do it again.

Answer 2

Also broken: https://stackoverflow.com/users/1/web.config