Originally posted by zzeitg Once I release the AF button, the focus lock is gone.
No it is not. The focus does not change just because you let go of the button. If you have back button (AF button) set to focus and shutter release button set to release shutter only then you focus with the back button, let go of the button and shoot as much as you want. The focus will not change.
If you have the camera in AF.C then as long as you are holding the AF button down then the camera will keep re-focusing even if you or the subject moves, but once you let go the AF button focusing stops at the last focused point.
Edit: Let me rephrase that, the 'lock' is gone but the focus is still the same, the lens has not changed the focus point.