In the update notes for the new version, ShipStation says this about the "split and combine shipments improvements":
This new process also more accurately represents what our merchants are actually doing. You are either fulfilling items from a single order separately, or you are fulfilling items from separate orders together.
Not sure where you got your information from but that is definitely NOT what I need to use the split order feature for. How about orders that need to be split because we can not fulfill the entire order?? How are we to accomplish that? There is no ability to edit the invoice even if we use the split shipment feature and cancel the other part of the shipment.