X-100 auto-ISO

I am in Aperture Priority with auto-iso set to 200-800 with a min shutter speed of 1/160.

I am getting pictures with speeds much faster than 1/60 (ie: 1/640) at ISO 800. How is this possible? The camera is supposed to lower speeds up to 1/60 BEFORE raising ISO.

I wonder how auto-iOS really works in the X100.