With a TNT block in a moving Minecart with TNT item, the TNT block will visually change the orientation it is in, depending on whether is is derailed or what direction the minecart is facing. TNT should not be able to orientate itself.

To replicate:
1. Make a short track, with turns and open ends.
2. Place the TNT cart on the rails, and push it along.
3. While you are doing that, observe how the rotation of the top "wick" of the TNT sometimes changes when you complete a turn.
4. Also observe the same effect between the cart rolling on and off the track, even if it is in a straight line.
5. Repeat, noting the changes again, until the TNT is mishandled and blows up. (optional)