The bug

When a player shoots himself with a bow he will be damaged by his own thorns enchantment.

How to reproduce

1. Use the following command and equip the chestplate

   /give @p minecraft:diamond_chestplate 1 0 {ench:[{id:7s,lvl:32767s}]}
   

2. Shoot yourself
   → Your chestplate will break and you will die because of the thorns damage

Possible solution

The following is based on a decompiled version of Minecraft 1.10 using MCP 9.30.

This could probably be tested in the methods net.minecraft.enchantment.EnchantmentHelper.applyThornEnchantments(EntityLivingBase, Entity) (better?) or net.minecraft.enchantment.EnchantmentThorns.onUserHurt(EntityLivingBase, Entity, int).