Selling items to an NPC vendor and then right-clicking on the mega stack while the vendor is still open causes you to lose items

Video below shows the bug.

If you buy/sell items to an NPC vendor and then, while the vendor is still open, right-click on the mega stack, it will discard a max stack of that item. The item will disappear into nothingness. Player reported this after losing 10,000 scrap to the scrap vendor, the example shown in the video below. The same thing happens when buying pickles from the pickle vendor; right-clicking on this mega stack will cause the player to lose 100 pickles (a max stack.)