I have a game where I use physics sensor bodies to detect collisions. The world itself has a gravity of (0,0) and the bodies mimic the position of the sprite/bitmap they are attached to. In my implementation the physics bodies are meant to detect collision not simulate them. I noticed a problem when two sensor bodies collide. The first time the 2 bodies overlap they light up as if the collision is detected. After separating the 2 bodies and reoverlapping them, the collision is no longer detected. Only if I collide either with ANOTHER physics body do the 2 original bodies again register collisions with each other. After registering 1 collision the process needs to be repeated. Is this a known issue, implementation of box 2d or am I just missing out on something basic. I would provide my code but it is in several lua files. If you guys really want to see it I can follow up with a comment.