Had the hood pop open on my long-departed '71 Volvo 164 while cruising down the highway once: didn't even bend at the hinge attach points, let alone come back that far. Very effective air brake, as you might imagine.
  Fortunately I was in the outside lane, along a barrier, so I was able to stay lined up easily as I slowed down.
Quite a surprise, though- the latch had seemed fine to me last time I'd looked at it...