Actually 557 movement type is used for adjusting the stock in transit.
MMBE shows you the actual stock but MB5T shows the stock only with comparing the PO history tab (EKBE table),
To clear stock from MB5T, either you have to cancel the Goods Issue or you have to receive the goods from stock in transit by using the Purchase Order.
I've found an old thread, where its discussed in details MB5T Report..