I know what you mean. I noticed that too and figured out a 'workaround' for those intentionally misspelled words.Let it fix it for you and type a few words beyond. Then, go back and 'fix' the word to the corrupted spelling you desire. After typing the last letter in the word, hit the "End" key instead of the space key and resume your typing.
Word Perfect did the same thing, until I told it to add them to it's dictionary.
*chuckle*
You can also go up to the Edit button and hit "undo autocorrect" - and then add the word to your spellcheck.
I believe that if you backspace, fix the word, and then just keep typing, Word will not change the word again.
I like the autocorrect feature--besides fixing things like "hte" and "teh", it makes life easier on me--for instance, when I was writing my Ph.D. thesis, and my topic was a scientific word containing 25 letters and 7 other characters--yeah, autocorrect can be really nice.