How does the 'Use Viewport Render' setting behave (or not)?

Game Engine Game Engine Support and Discussion
1

When I render with the viewport, my keyboard is read to change the camera’s FOV and my display FOV updates as intended.
When I turn off the viewport rendering, then what is controlling the render updates? The camera’s FOV value is still being updated but the display does not.
thanks

edit: adding some details:
-The camera’s rotation updates fine, it’s just the FOV that doesn’t. It’s seems significant that the rotation applies to the Camera Object but the FOV applies to the Camera Data.