I found a weird behavior when working with fast loops and collisions that I've managed to isolate to a simple demo. The collision only works depending on the order of the objects in the event. Download my demo and press Space. I expect both objects to be destroyed. The events should be simple enough to follow.
I like having as good an understanding as possible of how the events in MMF work. This is certainly a case where I want to know why this behaves as it does.