This is a prime example (pun intended) of the back-focusing issues the 50L has. I aimed at his nose but the focus shifted backwards to the eyes. Even Beibei was alarmed.
I spent yesterday evening pouring through reviews / comments of this lens especially in fredmiranda's forums. I already knew of these issues but had hoped for the best. This morning, the lens was off to the service centre. I will try to tame this beast when it is back because I think the image quality is actually pretty smooth! The bokeh's magic.
PS: Photo processed with Elusive Action so these colours are not from the 50L but by action of Photoshop filters. Image is just to show back-focusing problem. :-P