selectedIndex (and all selectedIndices, didn't check these, though) must be increased/decreased by 1 on showing/hiding the root, but doesn't.

Failing test snippets

    @Test
    public void testShowRootItemAtIndexOn() {
        assertFalse("sanity: test setup such that root is not showing", getView().isShowRoot());
        int index = 3;
        getSelectionModel().select(index);
        assertEquals(getSelectedItem(), getView().getTreeItem(getSelectedIndex()));
        getView().setShowRoot(true);
        assertEquals(getSelectedItem(), getView().getTreeItem(getSelectedIndex()));
    }

    @Test
    public void testShowRootIndexOn() {
        assertFalse("sanity: test setup such that root is not showing", getView().isShowRoot());
        int index = 3;
        getSelectionModel().select(index);
        getView().setShowRoot(true);
        assertEquals(index + 1, getSelectedIndex());
    }