1.Improves writing/reading speeds when using UDMA 7-compatible CF cards.
2.Fixes a phenomenon where the IS function will not work when custom function C.Fn III-2 is set to [5: IS start] and the lens attached does not have an AF stop button. This is because custom function C.Fn III-2 allows users to assign IS start to the AF stop button on the lens.
https://www.usa.canon.com/cusa/support/consumer/eos_slr_camera_systems/eos_digital_slr_cameras/eos_5d_mark_ii?selectedName=ServiceAndSupport#DriversAndSoftwareCanon U.S.A. : Support & Drivers : EOS 5D Mark II
www.usa.canon.com
