We've asked our fulfillment partners to minimize shipping costs wherever possible. As a result this sometimes means it's less expensive for them to ship oddly shaped packages (think: posters in long tubes) or heavier packages (think: mugs) separately from other items, potentially using different carriers. It seems weird to us too, but we're told that minimizing the costs of shipping logistics is an art which is even stranger than making video games... so we decided to leave it to the professionals.