I'm getting an error. If I edit a unique item that someone has already bought, then no one can buy it, because an error message is displayed "This item is unique, and you already have one of this item in your cart. ". But in the cart there is no items.
It may not be about editing the item. I can not yet determine exactly why this problem occurs. Probably, if someone added a unique item to the cart, but did not pay for it, then no one else can buy the item while it is in the cart from another user.