explosions allow silverfish spawns

While playing a custom map a creeper explosion destroyed a large number of Monster Eggs, (silverfish blocks) but they still spawned silverfish. I recreated this in single player, creative and survival, with both creepers and TNT, in both cases silverfish were spawned when the blocks were destroyed.

According to the Minecraft wiki, breaking Monster Eggs with explosions shouldn't spawn silverfish:
"If the block is destroyed by an explosion (e.g., creepers, TNT, etc.), the Silverfish will die inside of the block,"
http://minecraft.gamepedia.com/Monster_Egg

Is this a bug, or is it intended? I couldn't find any mention of it having been changed.