Splash / lingering water bottle cannot hurt invulnerable blaze and enderman when player in creative mode.
Unlike the arrow, snowball, splash potion, lingering potion, ender pearl.
Code Analysis
Based off of Minecraft 1.11, MCP 9.35
When a blaze/enderman is hit with a water potion, the method net.minecraft.entity.projectile.EntityPotion.func_190545_n()
calls net.minecraft.entity.EntityLivingBase.attackFromEntity(DamageSource source, float amount)
which will return false if the entity is invulnerable.
If MC-78689 is a bug then this ticket is invalid