I've changed my system a bit, and the bug still happens of course.
Anyway, after creating an account, the user is eventually sent to a page called ~submission. In IE, the user will still get to that page even if they don't fill out the form. However, HFS luckily won't create their invalid account even if they're only missing one field. Another oddity is that at the top in the address bar, IE will display the correct redirected URL! If you go into the top of the address bar and click enter on the correct address of the new account page, IE will still stay on the validation page incorrectly. This must be some freakish IE problem. It happens in the new IE9 too . . .