Collision Detection not working

I have been using Unity for awhile now and have a pretty good handle on Collision Detection. So this has me stumped and I am wondering if I am missing something or (as I suspect) this is a bug. I am using Unity 4.5.4f1. I have tried creating a new project and I get the same results.

I have two 3D-Rigid-Bodies, they are EXACTLY the same except for they position.z -- When an object passes through the 1st rigid body it fires off it detection script (debug.log) just fine, then the same object passes through the 2nd rigid body nothing happens. If, while a collision is in progress, I enable gravity on the 2nd rigid body the detection script starts working. I can then disable gravity and it continues to work.

Also, when I enable gravity on the rigid body object it does not move. Any ideas would be appreciated.

[SOLVED - thanks MrSoad]

Added the following to my Update method:

 if (rigidbody.IsSleeping()) { rigidbody.WakeUp(); }