in game store bug

So I was just playing a game and i noticed if you were to buy an item at low health and if you were to undo it before you would get to full hp it will take health away. To be exact its the amount of health when you bought the item. So lets says you bought a long sword with 200 hp but if you were to let you health regain not to your max health and undo the items bought you would get placed back at 200 hp