TextEdit keeps saving .html file as .txt

As you know, you don't "save as..." files in Lion - Lion-compatible applications save a copy, and you don't get to specify what extension you want. So... I have all the proper preferences checked for TextEdit to properly open and manage .html documents ("ignore rich text commands in html files" is checked, "add .txt extension to plain text files" is unchecked. But every time I edit and then save an html source file, TextEdit changes the extension from .html to .txt. I've tried closing and opening the file again, both from the Finder and from TextEdit, and I see the same behavior. I can't figure out any way to keep the .html extension from within the appication - I always have to find the file in the Finder and manually change the extension back to .html after every time I edit it. Does anyone know how to fix this?