Maybe the start/stop works on the accelerator rather than the brake for all s-tronic boxes whether it has hill hold or not?
Sport 2.0 TDI 150 Sportback in Scuba Blue, alcantara/leather, advanced key, audi sound system, comfort pack w/ ACC and park assist, deselect sports suspension, auto-dimming & folding door mirrors, electric lumbar support, heated seats, hold assist, non-smoking pack, side & lane assist, reversing camera, storage & luggage pack, tech pack with audi connect, tyre pressure warning, towbar, variable headlight range control, xenon light pack
When test driving I didn't notice at what point exactly the engine kicked back in, it was so quick as so seamless I presumed it was when lifting the brake. It apparently takes 0.2 seconds to fire up!
A3 S-Line 1.8TFSI S-Tronic Daytona Grey, Tech Pack, Comfort Pack, B&O, Parking System Plus with reversing cam, HHA, Folding Mirrors, Interior Lighting Pack, Advanced Key