title: Why does __LASTFOCUS hidden field show up on only some ASP.Net pages?
body: <p>I'd been using the hookonfocus method from this article: 
  <a href="http://www.codeproject.com/KB/aspnet/MainatinFocusASPNET.aspx" rel="nofollow">http://www.codeproject.com/KB/aspnet/MainatinFocusASPNET.aspx</a></p>
  
  <p>to maintain focus during postbacks for certain .aspx pages.  However, I've noticed that several pages (and some very simple pages in a test project) don't include the hidden field __LASTFOCUS.  I'm trying to figure out which options I'm missing that will cause this hidden field to show up and be used to restore focus if I use javascript to keep __LASTFOCUS up to date when focus changes happen in an ASPX page.  </p>
  
  <p>Note: I'm using VS 2005/.Net 2.0 in case that makes a difference.  </p>