Canon has issued a product advisory for the 5D MkIII, admitting that the company's newest addition currently on shelves has some issues exposing correctly while the backlight is on. Canon is working on the issue, but has not yet stated anything specific about possible solutions...
It's important to note that this issue only happens in low-light situations and that it's different than a light leak, which is what not-so-uncommonly happens with lenses of various brands. Still, it's a big issue for some hoping to exploit the camera's great low-light capabilities; and hopefully Canon will find a solution soon. For a clearer idea of the issue, the video above shows an excellent example of the backlight-exposure problem.
Here's the full advisory:
"To Users of the Canon EOS 5D Mark III Digital SLR Camera
Thank you for using Canon products.
The phenomenon described below has been confirmed when using the Canon EOS 5D Mark III Digital SLR Camera.
Canon is now examining the countermeasures and once the countermeasures are decided, we will post the information on our Web site.
In extremely dark environments, if the LCD panel illuminates, the displayed exposure value may change as a result of the AE sensor’s detection of light from the LCD panel.
Canon EOS 5D Mark III Digital SLR Camera
Once the preparations are complete, we will be making an announcement on our Web site.
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.
Customer Support Operations
Canon U.S.A., Inc
Contact Information for Inquiries
Canon Customer Support Center
For additional support options: www.usa.canon.com/support"