Though the CTRL-Z suggestion is good, and though your particular case happens to be a corner you painted yourself into that you could easily paint yourself out of, I still think you might have a valid case for a bug report. I think that your description of your problem, if simplified, could be filed as a bug to google, for them to fix:

"Shouldn't autosave if the user's last text change was to select all and delete. User never wants autosave to save the deletion of a giant amount of text."