Index: wp-admin/includes/misc.php
===================================================================
--- wp-admin/includes/misc.php	(revision 11719)
+++ wp-admin/includes/misc.php	(working copy)
@@ -429,34 +429,6 @@
 }
 
 /**
- * Check if IIS 7 supports pretty permalinks
- *
- * @since 2.8.0
- *
- * @return bool
- */
-function iis7_supports_permalinks() {
-	global $is_iis7;
-
-	$supports_permalinks = false;
-	if ( $is_iis7 ) {
-		/* First we check if the DOMDocument class exists. If it does not exist,
-		 * which is the case for PHP 4.X, then we cannot easily update the xml configuration file,
-		 * hence we just bail out and tell user that pretty permalinks cannot be used.
-		 * This is not a big issue because PHP 4.X is going to be depricated and for IIS it
-		 * is recommended to use PHP 5.X NTS.
-		 * Next we check if the URL Rewrite Module 1.1 is loaded and enabled for the web site. When
-		 * URL Rewrite 1.1 is loaded it always sets a server variable called 'IIS_UrlRewriteModule'.
-		 * Lastly we make sure that PHP is running via FastCGI. This is important because if it runs
-		 * via ISAPI then pretty permalinks will not work.
-		 */
-		$supports_permalinks = class_exists('DOMDocument') && isset($_SERVER['IIS_UrlRewriteModule']) && ( php_sapi_name() == 'cgi-fcgi' );
-	}
-
-	return apply_filters('iis7_supports_permalinks', $supports_permalinks);
-}
-
-/**
  * Check if rewrite rule for WordPress already exists in the IIS 7 configuration file
  *
  * @since 2.8.0
 
Index: wp-includes/canonical.php
===================================================================
--- wp-includes/canonical.php	(revision 11719)
+++ wp-includes/canonical.php	(working copy)
@@ -39,7 +39,7 @@
 function redirect_canonical($requested_url=null, $do_redirect=true) {
 	global $wp_rewrite, $is_IIS, $wp_query, $wpdb;
 
-	if ( is_trackback() || is_search() || is_comments_popup() || is_admin() || $is_IIS || ( isset($_POST) && count($_POST) ) || is_preview() || is_robots() )
+	if ( is_trackback() || is_search() || is_comments_popup() || is_admin() || ( $is_IIS && !iis7_supports_permalinks() ) || ( isset($_POST) && count($_POST) ) || is_preview() || is_robots() )
 		return;
 
 	if ( !$requested_url ) {
Index: wp-includes/vars.php
===================================================================
--- wp-includes/vars.php	(revision 11719)
+++ wp-includes/vars.php	(working copy)
@@ -79,5 +79,31 @@
  */
 $is_iis7 = (strpos($_SERVER['SERVER_SOFTWARE'], 'Microsoft-IIS/7.') !== false);
 
+/**
+ * Check if IIS 7 supports pretty permalinks
+ *
+ * @since 2.8.0
+ *
+ * @return bool
+ */
+function iis7_supports_permalinks() {
+	global $is_iis7;
 
+	$supports_permalinks = false;
+	if ( $is_iis7 ) {
+		/* First we check if the DOMDocument class exists. If it does not exist,
+		 * which is the case for PHP 4.X, then we cannot easily update the xml configuration file,
+		 * hence we just bail out and tell user that pretty permalinks cannot be used.
+		 * This is not a big issue because PHP 4.X is going to be depricated and for IIS it
+		 * is recommended to use PHP 5.X NTS.
+		 * Next we check if the URL Rewrite Module 1.1 is loaded and enabled for the web site. When
+		 * URL Rewrite 1.1 is loaded it always sets a server variable called 'IIS_UrlRewriteModule'.
+		 * Lastly we make sure that PHP is running via FastCGI. This is important because if it runs
+		 * via ISAPI then pretty permalinks will not work.
+		 */
+		$supports_permalinks = class_exists('DOMDocument') && isset($_SERVER['IIS_UrlRewriteModule']) && ( php_sapi_name() == 'cgi-fcgi' );
+	}
+
+	return apply_filters('iis7_supports_permalinks', $supports_permalinks);
+}
 ?>
\ No newline at end of file