SAP differentiates between posting changes and transfer orders. Posting changes are used if nothing has to be moved, while transfer orders are the medium if a human has to move some material between bins.
What you described is a transfer posting, it just changes the ownership or an allocation or even a batch number, but the stock will not be moved physically.
Still SAP has not use the interim storage types to document such kind of transfers (posting changes) within the WM system. SAP does not just exchange a value in a quant.
Actually pretty similar to MM, where you also have 2 items in your material document, a reduction from the general stock and an increase of the sales order stock.
Such posting changes have to be processed in LU04 transaction.
In this LU04 transaction you can also find historic documents, those documents which you did not see in case the stock was from a single bin in your example, but check it, you can see that those also used the 922 storage type.
You need to talk to your WM counterpart to know about your local customizing.
You should also try yourself the LU04 or let the WM guy show it to you, so that you can see what you have to do there, as this is what you would need to replicate with a function module http://help.sap.com/saphelp_46c/helpdata/de/c6/f83a294afa11d182b90000e829fbfe/content.htm