The bug occurs when you set off TNT on top of either a fence or wall that is one block high (or whatever the hitbox height of the fence/wall is), the TNT will go straight through and land on the block below it before detonating. While this isn't game-breaking, I did discover this on accident.

How to Replicate: Place down either a fence or wall (I used an Oak Fence and Cobblestone Wall separately when replicating it), then place down a piece of TNT on top of the fence or wall, then set it off with either Redstone or Flint and Steel. (It's easier to replicate it via Flint and Steel compared to Redstone due to how the TNT "jumps" when primed).