I think you are encountering something with learning (i.e the increased ease when you play without looking) that is typical of deeply learned "muscle memory". The best example I know of this is how we walk down a flight of stairs. If you try and consciously control the shift of muscle and weight you will most likely fall. It is far more reliable to let the part of your brain that stores such long-learned complexities just do what needs to be done. The only time I have had trouble with well-known accompaniment is when I switch to an instrument that has a different scale length or a twelve-fret rather that a fourteen fret neck.

Michael