Several? I can't really recall any. Bianchi's crash is the only one that springs to mind and at that speed he was going under the tractor, nose or not.
The Tecpro's purpose is to slowly stop the car, which it did. He striked them at an unfortunate position, pretty much bang in the middle of two (or at least that's what it looks like), which is probably why they acted as they did. - Needless to say, those, as well as the car did their job and that's why he walked away from it.
Been a couple in GP2 this year, almost need the tecpro slightly lower than the surface so it can't get underneath.
I've got an odd feeling that we might be in for a good race tomorrow for some reason. (fingers crossed)