As you gain confidence in your typing, you tend to get sloppier. Always stay focused. I remember an accomplished typist saying that he always thought of each letter he was typing.

I'd rather not think about what I'm typing!  And that's the nice thing about being able to touch type, it just becomes a motor skill.  I think jumbling up letters is a natural consequence of faster typing.  I used to do the same thing even when hunt and pecking under Qwerty.  Perhaps you can train out the errors, but they don't happen all that often, for me anyway they are teh exception.

Edit: I didn't intend to slip that teh in there!  As an aside, there's that interesting phenenoma where if you keep the lead and trailing character, you can mix up the letters inside a word and still be able to read them.  It's probably why mistakes are so hard to find and correct.   Your mind just glosses over the errors.