BED not changing value after Qty change in MIGO

Hi,

When we are doing MIGO, a message is coming - Ensure that you can receive more quantity on the same excise invoice..after that we can't save the document.

Scenario:

First i do J1IEX, there Excise Invoice Quantity was 1216 and BED was 684.61 on it.

But when we do MIGO, We are just changing the Qty from 1216 to 1000. BED should calculate automatically after change the Qty but not changing.

After that when we are going to post the document, above mentioned message coming and document not saved.

Please guide..

Anil