Unfocusing and refocusing the window while game is paused executes 1 tick

To reproduce:
1. Ensure "Enable game pause" option is enabled
2. Go into a world and spawn a few mobs around you
3. Pause the game and click on a different window or the desktop
4. Click back onto the Minecraft window, and you will notice the mobs around you move slightly

I can attach a video if necessary.