That strange light issue I reported on not too long ago seems to have been resolved by Canon. Basically, while taking still photographs in very dark situations, the top LCD backlight would cause the meter in the Mark III to give a false reading, and the resulting exposure would therefore be incorrect. It looks like they are quietly fixing the issue on newer cameras, after they stopped shipments for a short period of time. If you are one of the lucky few who currently owns a 5D Mark III, then Canon has issued a response.
This is the response, courtesy of Canon Rumors:
To Users of the Canon EOS 5D Mark III Digital SLR Camera
Concerning the EOS 5D Mark III digital SLR camera, when the LCD panel illuminates in extremely dark environments, the displayed exposure value may change. Canon has concluded the investigation of this phenomenon, and this announcement informs you of our findings as described below.
In extremely dark environments, if the LCD panel illuminates, the displayed exposure value may change. However, based on the results of extensive testing this change in exposure value will not noticeably affect the captured image.
Canon EOS 5D Mark III Digital SLR Camera
*Products whose sixth digit in the serial number is 1 or 2 are affected.
For example, “xxxxx1xxxxxx” or “xxxxx2xxxxxx” ([x] represents any optional number.)
Under almost all shooting conditions (including dark environments) this phenomenon will not affect your captured images. However, if you would like Canon to inspect your camera, we will provide this service free of charge upon request beginning in mid-May. Please contact Canon using the information below to request service.
This information is for residents of the United States and Puerto Rico only. If you do not reside in the USA or Puerto Rico, please contact the Canon Customer Support Center in your region.
Please register the EOS 5D Mark III. By registering, we will be able to notify you via email when service updates are available. If you already registered, please ensure you are opted-in to receive the notification.
I'm glad Canon is not ignoring this (however minor it might be), and starting in May it looks like they'll take back your 5D Mark III body and fix the issue free of charge. It's good to see customer service actually doing what it was meant to do: provide service to customers. This doesn't seem to be a real problem in many shooting situations, and some have reported that they've seen it on other cameras. Regardless, if you buy a brand new camera, you should not be having these sorts of issues. If you feel like you could be shooting photos in dark places very often (like wedding photographers), I would send it back to Canon to get it fixed. For video shooters, this issue likely won't affect you at all, because the mirror is always up when taking video, and thus the light sensor is not affected by the top LCD backlight.
[via Canon Rumors]