So, you have a long, carefully contrived, SEO-friendly title for your pages (or really just a minimally descriptive one), but you don’t want that to show up in the navigation menus. There are a variety of complex ways to fix this, but one of the easiest is to use code like the following:

< ?php 
    $pages = get_pages("parent=0"); # returns parent pages
      foreach ($pages as $x_page) {
        $option = '<li><a href="'.get_page_link($x_page->ID).'">';
        $short_title = "";
        $short_title = get_post_meta($x_page ->ID, "nav_title", TRUE);
        if ($short_title == "")
                $option .= $x_page->post_title;
        else
                $option .= $short_title;
        end;
        $option .= '</a>';
        echo $option;
  }
 ?>

This usually ends up in header.php, and is a good patch for the problem. There are a couple of plugins that attempt to work around this by detecting whether or not you’re in the loop (the loop being the name for the main part of post/page printing), but invariably widgets screw this up somehow, and this solution seems to work a bit better for me, especially for a navigation header (hence the name.)