Sphere Collider set to Trigger acts as solid object

I'm trying to make a moving object with a spherical trigger, so that it can keep track of what objects are around it.

However, despite the fact that the Sphere Collider has the IsTrigger box checked, things still bounce off it as if it were a physical object.

I have an hierarchy as follows:

• Empty (object root)

• --> Empty called OuterCollider

• ----> Sphere Collider set to "IsTrigger"

I've tried adding and removing Rigidbody component to the object root, the OuterCollider object and other objects within the hierarchy. Nothing in that hierarchy is currently active except the empties and the sphere collider. And yet other rigidbodies bounce off it like it's a solid object. I've even tried closing the Unity editor and restarting it.

Any suggestions?