Some items doesnt get copied with header partner

Hi ,

I have a issue with an order, where when teh order header partners are redetermined, (ship to), some of the items on the order doesnt get copied with the new ship to.

There is a check box at the item partner screen which is been ticked only for the items where thsi change doesnt take place.

It indicates that 'Partner valid at item level, if this indicator has been activated, the partner is valid at item level.'.

Could someone please advice the reason as to whta the check box means as well as the reason as to why the header partner doesnt get copied to the line item partner.

Thanks,

Keshini