In MAPPINGS, when developing object, we'll build the working table from the edit view in source (and target).
When on that screen and pressing the "create working table", there's a "do you want to create...." message.
If the intention is that the button will always create a new working table (even if one already exists), then it's not working correctly.
If the intention is that the button will NOT overwrite an existing table, then the pop-up message should say so.