I used SQL to query node_hierarahy to find some nodes that did not have a parent (where parent = 0), manually mapped those nodes to a parent using the node edit form.The node edit form does show that these nodes indeed have parents and they do display in the parent's children list. So it's all functional.

But where I go back to the database and ran the same query I still get the same nodes with parent = 0. Is this normal?

I should add that I only mapped these node to a parent but no menu items were created for them.