Steam shopping cart is emptying itself
Solution 1:
I don't think it's because you've added funds to your wallet. I've added money to my wallet, and my cart was just as fine. However, it empties itself at some point in time, probably according to a specific schedule or when Steam updates its policy, etc. Mine's got emptied by Steam perhaps just as yours, about a day or two ago. But who knows, Valve works in mysterious ways.