(Tested in single player) If a TNT is primed and the player re-logs into the world, it doesn't save the player that ignited it. That leads to TNT kills not awarding XP, or the killer's name not showing up in death messages.
(Unlike other similar entities with an owner, TNT does not store its Owner in NBT in any way)

To view this bug:
  Spawn a mob that drops XP, or spawn a wolf and tame it.
  Ignite a TNT next to it.
  Restart the world before the TNT explodes.
  Once you log back in and the mob blows up, the XP will be missing or the wolf's death message won't show the killer.