Sales Order - Production Order Reservations- Standard Functionality clarification

Toddy_Boy

Dynamics Navision 2013 with lots of bespoke - because of this I'm not sure what the standard navision functionality would be so I'm looking for a little clarification if possible.

A sales order consists of 3 lines (different despatch dates), all for the same item, different quantities, all reserved against the same production order.

Line Qty
10000 10
20000 20
30000 30

First production order output for 7 reserves 7 against the first sales line.
Second production order output for 10 reserves 10 against the second sales line.

Is this the standard way Navision reservations work as I would have though the second output would reserve 3 against the first sales line and 7 against the second?

If the standard way is to split the reservations against lines 1 and 2 then I need to dig deeper into the bespoke code.

Any clarification appreciated.