Discussion losing joystick input if mouse clicks on another app or another part of Unity editor

I need to run my app in the Unity editor, not from a build. In this app, I'm getting the user's joystick input with

Input.GetAxis("JoystickVertical")

in the script.
But whenever I click on somewhere else than the Game view or another app, I lose the joystick input until I click back on the Game view again. Why is this happening? Is this a bug? How can I prevent losing the user's joystick input when I click on somewhere other than the Game view during gameplay?