Strange Behavior in Manual Focus with XE-1
The camera is just giving you a depth of field preview, it isn't auto-focusing. The camera keeps the aperture blades open fully while composing a shot, when you push the shutter release half way down it adjusts the aperture to what you have set on the lens. Notice that it doesn't do this when you have the lens set to the widest aperture.
Fuji X-E1 w/ 35mm f/1.4 and 18mm f/2.0
Canon 5D MkII w/ 24-70 f/2.8, Sigma 50 f/1.4, Canon 85 f/1.8, etc, etc...