Yes, this is normal. Like walking, lifting your heels off the pedals is a natural motion. Two things determine how much your foot comes off the pedal; body position and pedal articulation. With body position the more you lean forward the more your foot comes off the pedal. Pedal articulation, or how much the pedal pivots, will be impacted as the pedal follows your foot’s movement. It is natural for the heel to rise faster than the toe when going forward.