Same here, and I agree it's puzzling. Especially not wanting to go to bed. With most of my behaviors that don't have an obvious motivation, I can think it through and figure out what's going on, but not with this one.
I wonder if it's a latent anti-bedtime reaction from childhood?
Speaking of which, why do all "good" American parents enforce bedtimes? I would think that if they enforced the getting-up time, the kids would take care of the getting-to-sleep part on their own.
Full essay: http://www.gwern.net/Melatonin