Don't unselect already selected childs

program/js/list.js

@@ -1021,6 +1021,7 @@ drag_mouse_move: function(e)
             if ((r = this.rows[row.uid])) {
               if (!r.depth || r.depth <= depth)
                 break;
+              if (!this.in_selection(r.uid))
                 this.select_row(r.uid, CONTROL_KEY);
             }
           }