When sprinting, or anything, in 1.7+ you loose hunger/saturation at a much, much higher rate than in 1.6.4 and below. This wasn't listed as one of the features so it seems like it'd be a bug.
The rate of loosing hunger bars in 1.7.2 when not hungry seems to be identical to the rate in 1.6.4 when hungry. And in 1.7.2 when hungry you lose hunger at an even faster rate.
This youtube clip shows the issue in action: