FRTH Getting wiped out when maintaining order with a different Ship To number

I reasearched this on the oracle site and found (Doc ID 987767.1).  A statement made in this document makes it sound like the FRTH value should not get wiped out if the order is maintained with a different Ship To.  In my scenario I enter an order with a FRTH value manually populated.  After placing the order, I maintain the order and change the Ship To number in the header.  The FRTH ends up getting blanked out.  While it's true that the FRTH defined on the new Ship To record is in fact blank, it seems like the field should not be getting updated because it already contained a manually entered