title: Very strange wordpress behaviour with shortcode
body: <p>I'm witnessing a very strange phenomenon on one page (http://can.org.uk/training/training-diary) on our wp site. The page exhibiting the strange behaviour is processed by single.php and the post has a shortcode in it. The shortcode is:</p>
  
  <p>[tcal tag=course]</p>
  
  <p>This shortcode should generate a table containing all the posts tagged with 'course' within the current category. Now I know the code works as it was working this morning and, if I put an echo at the bottom of the shortcode function then I can see that the relevant table hase been built and is begin returned by the function.</p>
  
  <p>Problem is, the page simply shows as blank ... nothing at all shows up. </p>
  
  <p>Also, even stranger still, after just checking again, now the entire site shows as blank ... e.g. if I go to the home page <a href="http://can.org.uk" rel="nofollow">http://can.org.uk</a> then I see nothing at all - at least on my home laptop it shows blank, on my work pc it seems to work just fine (except for the page mentioned earlier). </p>
  
  <p>I can log into the dashboard and all looks just fine. 
  I don't have any plugins installed.</p>
  
  <p>Anyone know what could be going wrong here?</p>