dropping items while tapping the swap offhand item while having a non stackable item on one hand creates a visual bug

What I expected to happen was...:
the item in the offhand to drop and the main hand to be empty

What actually happened was...:
the item in the main hand appears to have duplicated onto the offhand and main hand

Steps to Reproduce:
1. have a number of stackable items in the main hand and a non stackable item in the offhand

2. press the drop key and the swap item offhand key at the same time