YES!!!!!!!
i've never complained about this happening before, but I'm so glad to see someone post it.

i've had this happen (when not using terrains) in the hyb-ray when rendering large images in the background.

basically, i hit render and then switched apps using apple-tab, did some work for a while, popped back into C to check the progress, and it looked like there were giant areas of jpg compression.

granted this was before the 2.1 patch, and I haven't tried replicating it. I just render finals at night now, and sleep while the computer works.

-pix