Canon has cautioned on its website that the 2.0.3 firmware update for the EOS 5D Mark II DSLR has audio problems. When users change the manual recording levels for the C1, C2, or C3 modes and Sound Recording is set to Manual, the camera will not record sound along with video if power is turned off manually or automatically after idling. Canon urges 5D Mark II owners who have already downloaded the firmware to mitigate this issue by setting Sound Recording to Auto.
