After you file

Wow.  That's a horrible and sickening flaw that TT will essentially allow you to destroy a return that's already been filed.  Just as reprehensible is the lack of warning that you're getting ready to do so.  It would make much more sense to  freeze (i.e. make read-only) a filed return and let you work with a copy to amend.  But thanks for the information, I appreciate it.