When I use the /fill Command to turn a region containing Mob Spawners into another block such as Air or Cobblestone, the Particles continue to be emitted by the Spawner even though it is no longer there!

What I expected to happen was:

The Particles fade out, and that becomes the end of that.

What actually happened was:

The particles linger until I rejoin the world.

At some point all of the blocks in the attached image contained a Mob Spawner.