The bug

When using a carrot on a stick while riding a pig the carrot on a stick always acts as if it was not successfully used client-side. This means that if you hold an item in your offhand, that item will be used as well.

How to reproduce

1. Spawn a pig and give it a saddle
2. Mount it, put a carrot on a stick in your mainhand and another item with right click ability in your offhand, for example a fishing rod
3. Right click with the carrot on a stick
   → You will see that the fishing rod was used as well

Code analysis

Based on 1.11.2 decompiled using MCP 9.35 rc1

The method net.minecraft.item.ItemCarrotOnAStick.onItemRightClick(World, EntityPlayer, EnumHand) always returns EnumActionResult.PASS client-side.