This is from canon-europe...
FAQ: EOS 5D Mark III - Quality Issue Announcement
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 decided on our service policy to address this phenomenon, so we would like to inform you of the details as described below.
EOS 5D Mark III Digital SLR Camera whose sixth digit in the serial number is 1 or 2.
For example, “xxxxx1xxxxxx” or “xxxxx2xxxxxx” (x represents any optional number)
In extremely dark environments*, if the LCD panel illuminates, the displayed exposure value may change. However, when shooting with a lens attached, this change in exposure value will not significantly affect the shooting results.
* Some examples of a dark environment are as follows:
1. When the body cap is attached
2. When the lens cap is attached
The products affected by this issue will be inspected and repaired free of charge after 10 May 2012 therefore you are kindly requested to contact one of our authorised service facilities.
If you have any further enquiries, please contact us using the e-mail support or telephone support option.
We offer our sincere apologies to customers who have been inconvenienced by this. Canon strives to provide the highest quality products to our customers, and we spare no effort in our quality management to make sure our customers use our products with confidence. We hope our efforts will earn your understanding.