Hi Richard;
I have not personally used this feature for over a decade now. Its hard to say if this feature worked 100% for DB updating in the old PowerSoft days (who originally wrote the feature). All-in-all, this feature was not used in a lot of applications that I can remember. However saying that, I would suggest that you open a Support ticket for this issue as it certainly should work for generating Insert/Delete/Update DML IMHO. Who knows what changes were made in this area by Sybase and/or SAP that may have broken something in the RowsToDisk feature DB update wise.
With the above being said, it should be easy to workaround the issue. Just use the RowsToDisk DWO as a "WIP" (work in progress) pick list for the App user. When your App wants to update something, use a second DWO that has a retrieval argument on the same table utilizing a key. Pass the key from the RowsToDisk DWO to the 2nd DWO and let it perform the DB updating (insert, Update, Delete) of that particular row, then commit. Food for thought.
HTH
Regards ... Chris