I’ve personally seen a rear (external cam) QR shoved open mid ride. Exactly as described above. Two I experienced riders in close formation. Front one slowed suddenly for a car. Rear rider overlapped wheels and turned away to the left at the last minute. It swung open the rear QR of the rider in the front. Fortunately it was a vertical dropout bike, so nothing catastrophic happened. The front rider felt something off, and slowly came to a stop to fix the issue. This could also get a front QR that was forward facing, though you seldom see that.

I’ve also seen a front QR open, though the bike was static. Bike parked at a bike rack. Someone else trying to force another bike into a not big enough space, and opened the backward facing front QR. Easy enough to find if you do a basic pre-ride check, but less so if you don’t.

I put my front QR parallel to or just behind the fork as shown above, depending on QR type and handle shape. The rear I tuck between the stays.