Invulnerable tag doesn't work for Silverfish

Using this command:

/summon Silverfish ~ ~ ~ {Invulnerable:1,Attributes:[{Name:generic.movementSpeed,Base:0}]}

the Silverfish summoned is meant to be invulnerable.

However, the silverfish can be punched to death anyway.
The tag works for the other mob, but not for the silverfish.