Sometimes during normal execution, gtk_tree_view_clamp_node is run after
gtk_tree_view_scroll_to_X.  If gtk_tree_view_scroll_to_X has queued the
scroll, clamp node will preserve the destination, but will not maintain the
alignment.  I think the function would be improved if it checked for a
queued alignment as follows:

static void
gtk_tree_view_clamp_node_visible (GtkTreeView *tree_view,
                  GtkRBTree   *tree,
                  GtkRBNode   *node)
{
  GtkTreePath *path = NULL;
  gint use_align = 0;
  gfloat row_align = 0;
  gfloat col_align = 0;

  /* We process updates because we want to clear old selected items when we
scroll.
   * if this is removed, we get a "selection streak" at the bottom. */
  if (!GTK_WIDGET_REALIZED (tree_view))
    return;

  if (tree_view->priv->scroll_to_use_align) {
     use_align = 1;
     row_align = tree_view->priv->scroll_to_row_align;
     col_align = tree_view->priv->scroll_to_col_align;
  }

  path = _gtk_tree_view_find_path (tree_view, tree, node);

  if (path)
    {
      gtk_tree_view_scroll_to_cell (tree_view, path, NULL, use_align,
row_align, col_align);
      gtk_tree_path_free (path);
    }
}