Parent lost expand/collapse option for its children

After an editor trashed a parent page which I then restored, the parent page no longer has the expand/collapse option for its children. The children display indented below the parent, but its as if the parent is always expanded. Furthermore, the icon for expand/collapse is missing on the parent. That being said, the navigational structure of the site is functioning correctly and the linking hierarchy is correct. It is in the Nested Pages view where the issue is evident. Is there a way I can manually tweak something to get the expand/collapse back for a parent page?