My son was seeing really bad performance in MC tonight. I created a new world and noticed that the RenderDistance was in the left most position, but showed 128 chunks. That might explain the performance issue. I moved it, and then it would show the left most position as 8 chunks - which is correct, it goes up to 72 chunks on the right I think.

I haven't been able to reproduce the issue though. Perhaps after an update it will only happen the first time it is played and then the render distance is fixed (once adjusted?).