Certain neutral mobs can damage you even when the difficulty is set to Peaceful. When aggravated, they should show the attack animation but not cause any damage. Instead, they can inflict damage and kill you.

Steps to Reproduce:

• Start a survival world with cheats enabled
• Summon a Polar Bear, and attack it
• Player will take damage when it retaliates

Mobs affected:

• Iron Golem
• Wolf
• Polar Bear
• Shulker (These can continue to attack for a short time after the game is switched from a higher difficulty to peaceful, but may be a separate bug)