Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 19734)
+++ wp-includes/formatting.php	(working copy)
@@ -177,6 +177,20 @@
 		return '';
 	$pee = $pee . "\n"; // just to make things a little easier, pad the end
 	$pee = preg_replace('|<br />\s*<br />|', "\n\n", $pee);
+
+	// Save pre tags
+	$pre_blocks = array();
+	if ( preg_match_all( '/<pre[^>]*>(.*?)<\/pre>/is', $pee, $matches ) ) {
+		$counter = 0;
+		foreach ( (array) $matches as $match ) {
+			$token = '<WPPre_' . $counter++ . ' />';
+			$pre_blocks[$token] = $match[0];
+			$pos = strpos( $pee, $match[0] );
+			if ( false !== $pos )
+				$pee = substr( $pee, 0, $pos ) . $token . substr( $pee, $pos + strlen( $match[0] ) );
+		}
+	}
+
 	// Space things out a little
 	$allblocks = '(?:table|thead|tfoot|caption|col|colgroup|tbody|tr|td|th|div|dl|dd|dt|ul|ol|li|pre|select|option|form|map|area|blockquote|address|math|style|input|p|h[1-6]|hr|fieldset|legend|section|article|aside|hgroup|header|footer|nav|figure|figcaption|details|menu|summary)';
 	$pee = preg_replace('!(<' . $allblocks . '[^>]*>)!', "\n$1", $pee);
@@ -207,8 +221,11 @@
 	}
 	$pee = preg_replace('!(</?' . $allblocks . '[^>]*>)\s*<br />!', "$1", $pee);
 	$pee = preg_replace('!<br />(\s*</?(?:p|li|div|dl|dd|dt|th|pre|td|ul|ol)[^>]*>)!', '$1', $pee);
-	if (strpos($pee, '<pre') !== false)
-		$pee = preg_replace_callback('!(<pre[^>]*>)(.*?)</pre>!is', 'clean_pre', $pee );
+	
+	// Replace pre tags
+	if ( !empty( $pre_blocks ) )
+		$pee = str_replace( array_keys( $pre_blocks ), array_values( $pre_blocks ), $pee );
+
 	$pee = preg_replace( "|\n</p>$|", '</p>', $pee );
 
 	return $pee;