Karthus shop bug

Heey so I am unsure if this is a bug 100% but last game i was playing Karthus and was trying to buy a Void staff last item, i had prior bought theww new item that gives 100ap and move speed (idk on the name i dont use it much sorry ps its the ping spheere thingy). Upon realizeing i didnt not have a void staff i sold the item and tried to buy a void staff the game decided upon clicking the void staff what iu really wanted was an aether wisp. I then reloged to see if it was lag problem preceeded so then instead of clicking the void staff on the Recomended items Tab i searched it and was gfive then aether wisp. I am unsure if this is a bug or a one time glitch so i put it here bc its annoyingly difficult to kill a trundle and nasus with no magic pen.