When a Mob Spawner block, (Found in Mine Shafts, Dungeons, Etc.) is destroyed with a block of TNT, it appears to still have the tiny fire effect, floating in the air.
I am uncertain of if this only works with the Cave Spider spawner, and may only be the TNT that causes this, but it was something that caught my attention. I am also uncertain if this happened in older versions of MineCraft.