Silverfish inside spawners remain when spawner is broken.

When a naturally spawned Silverfish spawner is broken in Survival mode, the small silverfish inside does not dissapear.

What I Expected: When the spawner was broken, the Silverfish inside would dissapear.
What Happened: The silverfish remained after the spawner was broken.
Steps to Reproduce: Locate a stronghold using Ender Eyes and break the silverfish spawner in survival mode.