Karthus Bug [GAMEPLAY]

I had just died on Karthus, and while i was in my "death defile" passive I spam-clicked To buy Rylais at the shop. However, as soon as my passive ended and the shop allowed buying, i bought two rylais on accident and i couldnt refund the second rylais.

Step 1) Gain some gold Step 2) Die on Karthus Step 3) spam click buying an item in the shop during passive Step 4) overbuy the item and not be able to undo the purchase