Index: wp-includes/class-phpmailer.php
===================================================================
--- wp-includes/class-phpmailer.php	(revision 11072)
+++ wp-includes/class-phpmailer.php	(working copy)
@@ -1403,6 +1403,15 @@
   }
 
   /**
+   * Callback for converting to "=XX".
+   * @access private
+   * @return string
+   */
+  function EncodeQ_callback ($matches) {
+    return "=".sprintf("%02X", ord($matches[1]));
+  }
+
+  /**
    * Encode string to q encoding.
    * @access private
    * @return string
@@ -1413,15 +1422,18 @@
 
     switch (strtolower($position)) {
       case 'phrase':
-        $encoded = preg_replace("/([^A-Za-z0-9!*+\/ -])/e", "'='.sprintf('%02X', ord('\\1'))", $encoded);
+        $encoded = preg_replace_callback("/([^A-Za-z0-9!*+\/ -])/",
+                                         "EncodeQ_callback", $encoded);
         break;
       case 'comment':
-        $encoded = preg_replace("/([\(\)\"])/e", "'='.sprintf('%02X', ord('\\1'))", $encoded);
+        $encoded = preg_replace_callback("/([\(\)\"])/",
+                                         "EncodeQ_callback", $encoded);
+        break;
       case 'text':
       default:
         /* Replace every high ascii, control =, ? and _ characters */
-        $encoded = preg_replace('/([\000-\011\013\014\016-\037\075\077\137\177-\377])/e',
-              "'='.sprintf('%02X', ord('\\1'))", $encoded);
+        $encoded = preg_replace_callback('/([\000-\011\013\014\016-\037\075\077\137\177-\377])/',
+                                         "EncodeQ_callback", $encoded);
         break;
     }
 
Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 11072)
+++ wp-includes/formatting.php	(working copy)
@@ -773,6 +773,18 @@
 }
 
 /**
+ * Callback used to change %uXXXX to &#YYY; syntax
+ *
+ * @since 2.8?
+ *
+ * @param array $matches Single Match
+ * @return string An HTML entity
+ */
+function funky_javascript_callback($matches) {
+	return "&#".base_convert($matches[1],16,10).";";
+}
+
+/**
  * Fixes javascript bugs in browsers.
  *
  * Converts unicode characters to HTML numbered entities.
@@ -788,9 +800,10 @@
 	// Fixes for browsers' javascript bugs
 	global $is_macIE, $is_winIE;
 
-	/** @todo use preg_replace_callback() instead */
 	if ( $is_winIE || $is_macIE )
-		$text =  preg_replace("/\%u([0-9A-F]{4,4})/e",  "'&#'.base_convert('\\1',16,10).';'", $text);
+		$text =  preg_replace_callback("/\%u([0-9A-F]{4,4})/",
+					       "funky_javascript_callback",
+					       $text);
 
 	return $text;
 }