TreeView: unexpected behaviour of getRow(TreeItem)

my expectations are that getRow returns a non-negative index if contained in the expandedDescendants of the root, or -1 if not. Something like:

     if (tree.getRow(item) > -1) {
          assertTrue(tree.getRow(item) < tree.getExpandedItemCount();
     }

Implying that the method is kind-of invers of getTreeItem, such that:

     int row = tree.getRow(item);
     if (row > -1) {
         assertSame(item, tree.getTreeItem(row));
     }

Actual behaviour seems to be to return the row where it would be if its parent were expanded . While not entirely certain if my expectations are correct (doc is a bit vague), can't think of a use-case where the actual behaviour would be useful. Or the other way round: if this is the intended behaviour, the api is incomplete, as we need some means to convert between tree row coordinates (== rows that can be selected) and the tree structure.

Test snippets (complete test at: https://github.com/kleopatra/swingempire-fx/blob/master/fx8-swingempire/src/test/de/swingempire/fx/scene/control/TreeViewTest.java)

    @Test
    public void testRowLessThanExpandedItemCount() {
        TreeItem child = createSubTree("child");
        TreeItem grandChild = (TreeItem) child.getChildren().get(rawItems.size() - 1);
        root.getChildren().add(child);
        assertTrue("row of item must be less than expandedItemCount, but was: " + tree.getRow(grandChild),
                tree.getRow(grandChild) < tree.getExpandedItemCount());
    }

    @Test
    public void testRowOfGrandChildInCollapsedChild() {
        // create a collapsed new child to insert into the root
        TreeItem newChild = createSubTree("added-child");
        TreeItem grandChild = (TreeItem) newChild.getChildren().get(2);
        root.getChildren().add(6, newChild);
        // query the row of a grand-child
        int row = tree.getRow(grandChild);
        // grandChild not visible, row coordinate in tree is not available
        assertEquals("grandChild not visible", -1, row);
        // the other way round: if we get a row, expect the item at the row be the grandChild
        assertEquals(grandChild, tree.getTreeItem(row));
    }