title: Page tab redirecting to page tab URL, but only for some users
body: <p>I have a PageTab configured to serve content from my own web server (within an iframe).</p>
  
  <p>The script on my web server just gets the signed_request variable (passed from Facebook), and checks to see if a user has liked the page or not, and displays content accordingly. This is working for MOST users, but some users are reporting that Facebook is redirecting their browsers directly to the URL that the page tab points to (the URL on my web server).</p>
  
  <p>I have put debug in place, and sure enough, users are accessing the URL directly. Not cool.</p>
  
  <p>This is purely a PageTab, nothing to do with Canvas at all. Anyone have any ideas why this would be happening?</p>