Another possibility is photo software. I found sometime ago on a trial with Corel Photoalbum 6 that it can corrupt The exif when you add Keywords. I discovered this when my sons printer refused to print it correctly until the exif was removed. Looking closer some images given Keywords had various parameters wrong.

I have a Cano 20D And I too have noticed this problem, not only on this forum but also when using Photoshop File Browser. I rang Canon's help line and their reply was to the effect that 'Our softwhere does not support Photoshop.'

I have noticed on my shots that are in the Gallery (taken with 350d) the last two shots I have taken just shows the actual focal length with no crop factor shown at all whereas the earlier shots show an incorrect crop factor - something around 7:1.
Could this be something to do with the Camera firmware as I updated a few months ago?