Because I'm tired of having to edit people's posts to close their HTML tags, and because TypePad has refused to fix this problem, I have decided to turn this option off.
The TypePad programmers waste their time creating Compose Post editors that work worse the the original editor, but they refuse to fix known bugs that have been outstanding for years. How hard can it be to check input for unclosed HTML tags? Blogger does it, and Blogger is a free service. Shame on you Typepad.