Mob Spawner fire particles remain after spawner removed by /fill

I had several mob spawners (spawning creepers, incidentally) in a structure. When I removed the structure using /fill, with air as the block to place, the spawners were removed, but the fire particles remained. Even when I put them inside of another block, and break the block, the particles remain indefinitely.

Creepers also continue to spawn out of the particles as normal.