Why can't my relay antenna control my drone?

I have a drone with a radio antenna broadcasting in a 5km radius. When it is near Base A (also 5km broadcast radius), I can control it. Base B is 4km from Base A and has a broadcast radius of 50km. My drone can successfully travel to Base B.

I would expect that if my drone is within 100m of Base B, I would be able to lower its broadcast radius to ~300m and still have a two way channel, using Base B as a relay; however when I lower the drone's broadcast radius below the distance to Base A, I can no longer control its gyro and thrusters from Base A. Surprisingly, I can still see the camera. Why is this?

I have also discovered that I can still manipulate the drone by overriding the thrusters and gyro; it's only using the mouse and keyboard that's affected by this limitation. Is this a bug?