Twice now while heel-toeing, my knee would hit my key chain and inadvertently turn off my ignition. Luckily the clutch is depressed during HT but the power steering goes away. No accidents happened but just be careful, especially if you have a large key chain. John

 

Try using more of the side of your foot instead of your actual heel. I never shut the engine off but I've bumped the ignition a couple of times when I was practicing.

 

I don't heel-toe but I've done the same thing autocrossing. The key is removed from the fob before any runs now...