Yes, they are supposed to be filled in.
OK, I think I see what is happening.
Can you try authorizing again, but this time DON'T save the form after the popup comes back and says it's been authorized. Instead, just close that popup, and reload the main page.
I think what's going on is that when I tested, I just authorized, then tried my front end form, and it worked. When you close that popup, it's supposed to set the fields on the form. But since that code was written, browsers have tightened up on security, and because it think Twitter opened that popup, it won't let it update fields on the main page. Which is OK if you don't save the form, because we've already stored those values in the database. But if you save the form, with those fields empty, it overwrites them.
Anyway .. try those instructions, it should work.
Meanwhile I'll try and fix it so it does save.
-- hugh