The bug

While looking at an armor stand you cannot use any item with right click ability (except a name tag).

How to reproduce

1. Place an armor stand and look at it
2. Try to use an item with right click ability, for example a fishing rod

Code analysis

Based on 1.11.2 decompiled using MCP 9.35 rc1

The method net.minecraft.entity.item.EntityArmorStand.applyPlayerInteraction(EntityPlayer, Vec3d, EnumHand) always returns EnumActionResult.SUCCESS for the client if the armor stand is not a marker one and the held item is not a name tag.

Important: To enable using an item in offhand while looking at an armor stand which is not wearing any armor or items when your mainhand is empty the method should also return EnumActionResult.FAIL at the code in the third nested if clause.

Fix

The fix provided in MC-83620 also fixes this.