OnTriggerEnter With 1 Rigidbody

Good afternoon,

I'm having an issue that may just be intended functionality; however, the documentation says otherwise. Here's the rundown (fairly straightforward):

I've got 2 objects in my scene. Both objects have a collider (both set to be 'Triggers'). I put a rigidbody on one object (the one that doesn't move). The other object does NOT have a rigidbody.

The problem is OnTriggerEnter() is not being called for the object that doesn't have a rigidbody. If I put a rigidbody on him also, the function is called. The documentation says that ONLY ONE of the objects needs to have a rigidbody for the messages to be fired off.

Side note: The reason I'd rather not put a rigidbody on the moving object is because I don't need any (minus of course this trigger collision detection) physics or collision detection on him, and there's going to be dozens (if not upwards of 100) of those objects in the scene. There's only 2-3 of the still object in the scene, so I'd rather leave the rigidbody on them since that's a pretty large difference (3 rigidbodies as opposed to 100).

In any case, is there something inherently wrong with what I'm doing? If I recall correctly, moving the rigidbody to the moving object (still 1 rigidbody between the two objects) seems to have worked. What gives?

Thanks in advance! -Matt