A few minutes after having selected the hot water cycle and the hot water entering the tub, the washer automatically switches to warm water without the selector being moved. If I don't intentionally close the cold water valve when this happens, I'd never have a true hot water cycle. Just doesn't make any sense!

Could be a bad temp selector switch. How new is it? Is it still under warranty?

Bought it 7/3/07 from Lowe's.

I would advise not attemping any repairs as you will void the warranty. Call for service.