[jQuery] load() works for html, not php

[jQuery] load() works for html, not php


http://reenie.org/test/jquerytest.html
This uses
$('#container').load('content.html'); to load content from an html
file
http://reenie.org/test/jquerytest.html
This uses
$('#container').load('content.php'); to load from a php file.
Why doesn' t the second one work? They are the same except for the
files being loaded.
If I change the second one to load the html file, it works fine.