Night Vision Potion Glitch

In MC 1.7.2, I tried using night vision potions to see things clearly (I mean, that's what they're supposed to do, right?). When I gave myself a splash potion of night vision (both times) and the regular potion (also both times) it would eventually make my screen go black, but Minecraft would still be working. You could still give yourself milk to make it go away, but still...