This is just an oddity I observed a while back when trying to look through my dismounted 12-40. Unlike other lenses I've owned which keep the aperture blades wide open the 12-40 seems to close them when the camera is turned off. I haven't seen anyone else comment on it, so maybe it's a more common occurrence among lenses than I realize. It's something I've been curious about though. Has anyone else noticed this? Is there a reason for it? Is my lens behaving oddly?