On unity when I move the mouse to the left side to unhide the dock, an orange border takes up half the screen and stays there until I maximize any of the window

On unity when I move the mouse to the left side to unhide the dock, an orange border takes up half the screen and stays there until I maximize any of the windows. This is extremely confusing, does anyone know if it's supposed to be a feature? Or if there's a way to turn it off? I asked in #ubuntu and nobody replied.