The problem with making this a settings option is that it means that users have to choose between having it one way or the other - all the time. What if you only want to alter the behavior for a particular action? I know that there are already a lot of shortcuts for this app, but it seems to me that adding a shortcut to temporarily override (e.g. ctl-shift-tab) the default behavior would allow users to chose what happens when the unindent rather than having it always work one way or another.