In some circumstances, NAV does not propose changes to existing orders when these could be replan to better suit the demand profile. An example, an started production which can be used to fulfill a demand. In this case, NAV will not change the production order. Why? Because it considers too late to change the production order since it already started. And, what would be other examples of order types which NAV treats the same? These are (as I understood):
- Orders already posted (purchase already receipt, transfer already shipped)
- Orders already in the warehouse
- Orders waiting for approval
- And, the example above production orders with status Started (with consumption or output postings)
 
There could be a debate here on if NAV should or should not allow this. But, the above is the current design. And, I would say that the above could be the better in most of the scenarios having in mind NAV should be the standard.