Steps to reproduce:
1. Spawn a shulker.
2. Give yourself a sword.
3. Enchant it with Fire Aspect.
4. Hit the shulker.

Expected result:
The shulker catches fire.

Actual result:
It acts as if the sword didn't have Fire Aspect at all. It works on other mobs, though.

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

It seems highly intended that Shulkers should be fire resistant, but to fix this, change this.isImmuneToFire to false or just remove the line.

    public EntityShulker(World worldIn)
    {
        this.isImmuneToFire = false; //previously set to true
    }