When in the Options menu, after changing your mipmap levels then leave the Options menu the mojang loading screen will pop up.

If you left the menu by pressing escape then the loading bar will appear (without the mojang logo) and you'll be able to look around but not any thing else.

If you press the done button the mojang screen will pop up with the loading bar.

If you pressed escape and are looking around with a loading bar in view then press escape again, you'll find the mojang screen will fade in.

If the mojang loading screen is on the screen. And you press escape the mouse arrow will disappear as if your opening and closing the Game menu.

I have not tested to see if it happens when you change any other settings. So good luck!