Index: wp-includes/functions-formatting.php
===================================================================
--- wp-includes/functions-formatting.php	(revision 3834)
+++ wp-includes/functions-formatting.php	(working copy)
@@ -521,9 +521,15 @@
 
 function zeroise($number,$threshold) { // function to add leading zeros when necessary
 	return sprintf('%0'.$threshold.'s', $number);
-	}
+}
 
 
+function preg_backslashit($string) {
+	$string = preg_replace('/^([0-9])/', '\\\\\\\\\1', $string);
+	$string = preg_replace('/([a-z])/i', '\\\\\1', $string);
+	return $string;
+}
+
 function backslashit($string) {
 	$string = preg_replace('/([a-z])/i', '\\\\\1', $string);
 	return $string;
Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 3834)
+++ wp-includes/functions.php	(working copy)
@@ -37,12 +37,12 @@
 		$datemeridiem = $wp_locale->get_meridiem(date('a', $i));
 		$datemeridiem_capital = $wp_locale->get_meridiem(date('A', $i));
 		$dateformatstring = ' '.$dateformatstring;
-		$dateformatstring = preg_replace("/([^\\\])D/", "\${1}".backslashit($dateweekday_abbrev), $dateformatstring);
-		$dateformatstring = preg_replace("/([^\\\])F/", "\${1}".backslashit($datemonth), $dateformatstring);
-		$dateformatstring = preg_replace("/([^\\\])l/", "\${1}".backslashit($dateweekday), $dateformatstring);
-		$dateformatstring = preg_replace("/([^\\\])M/", "\${1}".backslashit($datemonth_abbrev), $dateformatstring);
-		$dateformatstring = preg_replace("/([^\\\])a/", "\${1}".backslashit($datemeridiem), $dateformatstring);
-		$dateformatstring = preg_replace("/([^\\\])A/", "\${1}".backslashit($datemeridiem_capital), $dateformatstring);
+		$dateformatstring = preg_replace("/([^\\\])D/", "\\1".preg_backslashit($dateweekday_abbrev), $dateformatstring);
+		$dateformatstring = preg_replace("/([^\\\])F/", "\\1".preg_backslashit($datemonth), $dateformatstring);
+		$dateformatstring = preg_replace("/([^\\\])l/", "\\1".preg_backslashit($dateweekday), $dateformatstring);
+		$dateformatstring = preg_replace("/([^\\\])M/", "\\1".preg_backslashit($datemonth_abbrev), $dateformatstring);
+		$dateformatstring = preg_replace("/([^\\\])a/", "\\1".preg_backslashit($datemeridiem), $dateformatstring);
+		$dateformatstring = preg_replace("/([^\\\])A/", "\\1".preg_backslashit($datemeridiem_capital), $dateformatstring);
 
 		$dateformatstring = substr($dateformatstring, 1, strlen($dateformatstring)-1);
 	}
@@ -80,12 +80,12 @@
 		$datemeridiem = $wp_locale->get_meridiem(date('a', $i));
 		$datemeridiem_capital = $wp_locale->get_meridiem(date('A', $i));
 		$dateformatstring = ' '.$dateformatstring;
-		$dateformatstring = preg_replace("/([^\\\])D/", "\${1}".backslashit($dateweekday_abbrev), $dateformatstring);
-		$dateformatstring = preg_replace("/([^\\\])F/", "\${1}".backslashit($datemonth), $dateformatstring);
-		$dateformatstring = preg_replace("/([^\\\])l/", "\${1}".backslashit($dateweekday), $dateformatstring);
-		$dateformatstring = preg_replace("/([^\\\])M/", "\${1}".backslashit($datemonth_abbrev), $dateformatstring);
-		$dateformatstring = preg_replace("/([^\\\])a/", "\${1}".backslashit($datemeridiem), $dateformatstring);
-		$dateformatstring = preg_replace("/([^\\\])A/", "\${1}".backslashit($datemeridiem_capital), $dateformatstring);
+		$dateformatstring = preg_replace("/([^\\\])D/", "\\1".preg_backslashit($dateweekday_abbrev), $dateformatstring);
+		$dateformatstring = preg_replace("/([^\\\])F/", "\\1".preg_backslashit($datemonth), $dateformatstring);
+		$dateformatstring = preg_replace("/([^\\\])l/", "\\1".preg_backslashit($dateweekday), $dateformatstring);
+		$dateformatstring = preg_replace("/([^\\\])M/", "\\1".preg_backslashit($datemonth_abbrev), $dateformatstring);
+		$dateformatstring = preg_replace("/([^\\\])a/", "\\1".preg_backslashit($datemeridiem), $dateformatstring);
+		$dateformatstring = preg_replace("/([^\\\])A/", "\\1".preg_backslashit($datemeridiem_capital), $dateformatstring);
 
 		$dateformatstring = substr($dateformatstring, 1, strlen($dateformatstring)-1);
 	}