Stepping on a brake pedal when the brakes are split does not disengage the cruise, at least on my B7800 it doesn't. Just tapping the hydro pedal with your foot does disengage the cruise. The purpose of split brake steering is to give you the opportunity to make 180 deg. turns. For example, if you want to make an extremely sharp rt. turn, turn the steering wheel to the right and step on the rt. brake pedal. The rt. rear tire locks up and almost acts like a pivot and the left rear tire drives the tractor. There is almost no turning radius. This is also good for kind of "crabbing" the tractor if you're going across a hillside and you want to keep the front of the tractor kind of facing uphill, while the tractor is going across the slope. I've only tried steering with my brakes once with this tractor, just to see how well it works. It is hard on the tires, hard on the brakes, and really hard on your grass, but it does swing you around pretty quick.
Pat