contactTest always yields 2 contacts per object?

[DestroyerOfCities]

Hi! I have a little bullet app i slapped together (awesome library btw), and when I run through all my boxes and spheres and call contactTest with an addSingleResult that just increments a global, it always results in me getting 2 hits per object. For instance, i have a plane (which i don't call contactTest with) and I shoot a box out onto it; the global count will be 2 until the box goes to sleep (and it goes to 0). If I shoot a sphere out and hit the box, the count will be 4 (again until everything comes to rest).

Right now I'm just cutting the number in half, but I'm confused as to why I'm seeing this?