Item building confusion

I'm not sure if it's the same on Summoner's Rift, but when playing an ARAM, I noticed either a glitch or something Riot has missed. Very minor. When in the shop, clicking on a Giant's Belt, the item "builds" into Rylai's Crystal Scepter. But when buying or inspecting the Scepter, it does not require a Giant's Belt, and will not consume the item when bought.

I'm not sure if this is the same for other items, but this is just one I noticed.