I've got a front KCNC V-brake, and I when I first apply the brakes the 'bent spoke' (or spring) can be seen sliding slightly out of its locating hole at the top of the V-brake arm. It pushes back in with a click. I kept a close and wary eye on it at first, but it seemed not to move any further. However, a big guy squeezed my brake levers at the weekend, and the spring popped out completely!

Any idea what's causing this, and how can I stop it happening?