If you enter invalid input into the registration box, then hit tab, it tries to take you to the first field in the registration form. Since you haven't actually entered an email yet, it doesn't make it all the way to that next frame and it gets stuck. Hitting shift+tab takes you back to the main screen. Screenshot here: http://puu.sh/drYlr/cfba939d09.png
If you enter invalid input into the registration box, then hit tab, it tries to take you to the first field in the registration form. Since you haven't actually entered an email yet, it doesn't make it all the way to that next frame and it gets stuck. Hitting shift+tab takes you back to the main screen. Screenshot here: http://puu.sh/drYlr/cfba939d09.png