duplicated entries of Amount in LC in transaction MB5B

when our user runs the report of MB5B for certain materials which is a PO item with item category L (subcontracting) for a period of time the same material documents have two entries shown there in the output with the same duplicated value of Amount in LC.

This only happens for the valuated stock on movement type 121 at header material and its child material from movement type 543. As a result the header material from the PO item has wrong open value calculated.

Please help to give advice what is wrong here and how to make system change thus no duplicated entries shown there. I have go through the SAP note 2331848 with our finance consultant but seems it is not relevant on our case.