I'm also boggled with outer AF points.
I'm on my second 5dmk2 camera and it does the same as first one did.
If I have outer af point selected, camera doesn't focus. Not even hunting for focus.
Does it will all lenses.
I have to press for focus numerous times, recompose to make it works.
Same lenses works with outer af points on 500D and with 5Dc it was never the problem.
Or even with film EOS300.