This may not be a bug but a case of realistic expectations.
I seem to remember Ashley saying that if the speed is too great, and the objects it is meant to bounce off are too thin, then because it is checking for collisions 60 times every second, then the bullet could pass through the object instead of bouncing off.
So by my calculations (which could easily be in error) - if your bullet is traveling 2000px per sec, then it can travel 33 px in one tick. Considering the object it's meant to bounce off of is only 20 px wide, then it may jump straight over the object in one tick and not collide.
The answer was to increase the size of the object it collides with (even using an invisible collision object, for instance), or decrease the bullet speed.
I may be wrong, but that's how I remember it. Ashley is very busy at the mo, but I'm sure he'll see this eventually and correct me if necessary.