Changing Milestone date, Sales Order value getting changed

Hello,

I am encountering a problem wherein if somebody changes the milestone 'Basic fix. date' in project (CJ20N) then automatically in the sales order, the item value and the total order value both are getting changed to Gross value from Net value. The billing plan value gets increased.

But in printout of the order the correct net value is coming.

And if I change anything into the sales order (VA02) like any text field also, and then press enter, the sales order value comes back to original.

Can anybody suggest why this is happening.

Regards

Shubham