Crescent, I'm not getting the same results, so it might be your render/material settings.

The other two spheres are in all likelihood reflecting, unless you have the "Visible in Ray Tracing" option disabled in their Properties panels. You simply can't see their reflections from that camera angle; it's out of frame. Try tilting the camera down a bit.

Are you using FireFly's Draft mode or Production mode? What Quality setting are you using for the Reflect node in the Material Room? Do you have the same jagged effect with the other square props?

The image above uses Production mode, a one-sided square prop, and a Reflect-node Quality setting of 1.0.