Game wont allow me to sell my boots for a deathcap??????

Seriously, everytime i try to sell my boots, and buy a deathcap, it reverses it and my boots appear again. Get the fuck out of my shop rito.

EDIT: Sorry for being so harsh but this is INCREDIBLY bad design. I know it has something to do with that "accidental purchase prevention" or whatever, but things were fine before this change, and now I'm having all kinds of problems adjusting my build when it gets to late game. If people are seriously having that much trouble purchasing items properly in the shop, I highly doubt that is the most pressing issue with their gameplay.