I read your story, and I gotta agree with Canon on this one :) Truly an odd phenomenon. I tried a search on this, and came up with nothing concrete to help you out, but if I had to make a humble guess.... Id have to say that obviously it is the lens. The camera ccd sensor in RAW mode, is taking direct readings of your colors (as opposed to compressed lossy format), and recording this into a raw format on your media card. Im guessing here, but I reckon its a possibility that the optics in the lens is somehow causing 2 kinds of readings to be made on the sensor, and this is causing the camera to interpret it into both a colour and b+w version on the same image????? Just a guess.

"If toast
always lands butter-side down, and cats always land on their feet, what
happens if you strap toast on the back of a cat and drop it?"

Steven Wright