High CPU usage in develop mode when Lightroom 4.1 RC2 is idle or even in the background.

When working with RAW photos (Canon EOS 5D MkII) in Lightroom 4.1 RC2, and then leaving the application in develop mode and letting it sit idle or go to the background, the CPU usage stays high and my fan stays spun up at near maximum. As soon as I switch to library mode, the CPU usage goes back to nothing and fan spins down.