Some users were having problems on a community site that was implemented using WordPress+BuddyPress. After some testing the issue involved users visiting the site with Internet Explorer (IE). These users were receiving error pages instead of site content. Other web browsers did not have similar issues.

The cause of the problem turns out to be a confluence of issues:

• The site is hosted on a Windows+IIS server, a rare platform for WordPress (and even more so for BuddyPress) and one that probably doesn’t receive full attention during quality assurance testing.
• How WordPress performs redirects on IIS is a bit quirky. BuddyPress issues a lot of redirects so this redirect quirk comes into play quite often. The issue is that when WordPress needs to perform a redirect on IIS it returns a “refresh” header pointing to the new page rather than a “location” header.
• IE’s attempt to make the Internet more friendly; specifically IE’s use of “friendly error pages.” These friendly error pages replace the content delivered by the server (if that content falls below a certain size in KB).

Normally none of these issue are a problem by themselves and a web browser (including IE) will load the page indicated by the redirect. However, all three of the above issues taken together result in a situation where IE never sees the header refresh and so doesn’t redirect the user to the correct location.

The fix is fairly simple: change the headers that WordPress sends to include the standard “location” header. To do this you modify wordpress/wp-includes/pluggable.php@wp_redirect() so that it reads as follows (line 14 is new):

function wp_redirect($location, $status = 302) {
	global $is_IIS;

	$location = apply_filters('wp_redirect', $location, $status);
	$status = apply_filters('wp_redirect_status', $status, $location);

	if ( !$location ) // allows the wp_redirect filter to cancel a redirect
		return false;

	$location = wp_sanitize_redirect($location);

	if ( $is_IIS ) {
		header("Refresh: 0;url=$location");
		header("Location: $location", true, $status);
	} else {
		if ( php_sapi_name() != 'cgi-fcgi' )
			status_header($status); // This causes problems on IIS and some FastCGI setups
		header("Location: $location", true, $status);
	}
}