Shipment date is different from posting date problem

Hi guys my users in my company make wrong when they write shipment date it write it different from posting date by wrong

so that i want to make filtration in sales order when posting date written in sales header table it changed automatically in sales

line table shipment date how i make that

example

when my users need to post sales transaction in date before current date as 25-02-14 posting date take date today as 01-03-2014

but shipment date writing as 25-02-14 how i make shipment date as posting date as 25-02-14 with filte on table

or any way

i have dynamic nav 2009 r2 customer license