FYI save() has an optional second parameter with an array of fields to save. If you just want to save the title to the database just do
$model->save(true, array('title'));
true means “use validation before saving”, if you set it to false you can bypass validation (comes in handy if you’ve executed validation yourself before the save() call and don’t need to run it again).
Sorry, but I’m fairly certain this is not entirely true. The thing is that CActiveRecord inherits from CComponent, which in turn has a magic __unset which sets the property to be unset to null (see http://www.yiiframework.com/doc/api/1.1/CComponent#__unset-detail).
Since a field in an active record is not an actual field (i.e. it’s not explicitly defined in the class) the magic method will be called.
I can’t fathom why this would be different that unsetAttributes() though, as it clearly is …