Reordering Policies and Reservations

Hi there,
Our company has been researching and testing the Calculate Plan feature in Navision that allows for purchasing suggestions based on the different reordering policies. One topic that I have come across which I did not find an answer in the white papers, user manuals, and online research is why certain reordering policies allow reservations to be maintained while other reordering polices break the reservations to existing sales orders.

For example: The reordering policy of Order allows an existing reservation that was made by a user on a sales order to the requisition worksheet to be kept. While in the same scenario using a reordering policy of Lot-for-Lot or Maximum Qty. the reservation is broken.

Has anyone come across a reason why this is allowed to happen and why the reservations is not maintained regardless of the reordering policy being used?