Take no damage from TNT

i'm 17 dont let the bad grammar fool you
My wifi was off so I was trying stuff in single player one of the things I tried was putting a ton of tnt on one rail and standing beside it with prot 4 armor while it exploded, I took no damage tried without armor same result. Before this I was making 2 flight machines starting one slightly before the other with rs block attached and tnt on the other, to make the explosion bigger I used tnt minecarts I stacked a ton and a ton flew into the void and more blew up in the void. I was using Optifine when this happened but I can switch back and forth between that and 1.0.2 and still take no damage I realized I had messed up my world but that was not true. I decided to try something so I got on cubecraft and, it worked. I'm really not sure exactly what caused this bug, but I can't say I was sent looking for one. However I didn't think I would find something like this. Tnt plays a huge role in some minigames so I haven't told anyone else. I got a video demonstration https://www.youtube.com/watch?v=DEMqPeH9NhA&feature=youtu.be and If you need any more information you can email me jonasthemonkey@gmail.com or preferably call me 8284215582, it would be cool if a staff member could use team viewer to view my game for them self.
-side notes I tried it in other worlds still no damage alt account obviously no damage. my bad if wording is difficult to follow thanks for reading hopefully it is an easy fix so no one other than me will find it before its repaired.