What is happening to the Camera when I decrease the editor window height?

While the game is running and you decrease the editor window’s size, the scene scales to fit within the current camera view. What is happening here? As far as I can tell, none of the properties on the camera are changing. Is there a way to disable this behavior, so that the scene will NOT scale when the window size changes?

On the top left of the game view you have a drop down to chose the camera ratio. Yours if probably set to “Free” or “Auto” (sorry I can’t verify right now), which is why the ratio changes when you change editor window sizes.