The bug

Upwards or downwards facing dispensers or droppers do not offset the smoke particles they produce when activated.

How to reproduce

1. Place an upwards facing dispenser or dropper
2. Put for example bone meal into it and activate it
   → You will either not see any smoke particles or only a few ones barely appearing above the dispenser

Code analysis

Based on 1.11.2 decompiled using MCP 9.35 rc1

The method net.minecraft.dispenser.BehaviorDefaultDispenseItem.getWorldEventDataFrom(EnumFacing) only encodes the horizontal direction and the method net.minecraft.client.renderer.RenderGlobal.playEvent(EntityPlayer, int, BlockPos, int) only offsets the smoke particles in the horizontal directions. Instead the index of the EnumFacing value could be passed.