Everything fits together smoothly. The only even slightly noticable feature is a dimple on the mounting piece, but I don't see any use for this.
I've tried twisting the two parts of the glass bowl to no effect. I've also tried twisting the glass off the mounting piece, but the clearance is so s hort that this is almost impossible. I've also tried twisting the whole lig ht, but that seems to be moving the wires in the ceiling which I don't want to torque. Similarly, I've tried gently pulling and that didn't work.
Has anyone seen a fixture like this? Any idea how to open it?