What you are seeing is the first phase of a development effort which, at completion, will provide clients with full discretion as to which account segment (securities or commodities) excess cash is to be transferred as opposed to IB making that election.
As is the case with most development efforts, this is being driven by client requests ......
The bottom line here is that when the final phase of this effort is completed (estimated to be within the next 2-3 weeks), all clients will be in a better position to elect the transfer method which best suits their particular needs.