Only time my flat shipping rule works is if the two items have the same handling time. I sell both preorder items and items I have in stock. If a buyer buys two items I have in stock, it combines perfect. Same if they buy two preorder items. But, if they have one preorder item in cart and one item I have in stock in cart, it charges the buyer twice for shipping rather then it combining like it does for the other examples. This never happened before, and has only started happening about two weeks ago. Anyone have an idea on what is going on? Please help I am losing a ton of sales.
