Sales Order with Line Type W

If we create Sales Order with Line Type W ,the work order gets created with status 10.During creation of Sales Order ,i add an attachment and this attachment gets carried fwd to the work order which is good.

If i get again into the Sales Order and add a 2nd attachment for the same line ,then the 2nd attachment comes on the work order but the status of work order moves from 10 to 40.

Is this functionality correct or am i missing something in the set up?