Shop Undo button not working

Had a game where after buying either a (I don't remember exactly which item) pickaxe, ad/hp gauntlet, or a kindlegem I couldn't undo the purchase while sitting in the middle of the fountain. I understand how it's supposed to work; once you leave fountain you can't undo. But I never moved.... It might have been due to some rapid clicking of the shop button and the right click on my mouse. I've encountered lots of bugs today...