Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 15468)
+++ wp-includes/functions.php	(working copy)
@@ -232,21 +232,26 @@
 	if ( !is_string( $data ) )
 		return false;
 	$data = trim( $data );
+	if ( empty($data) )
+		return false;
 	if ( 'N;' == $data )
 		return true;
-	if ( !preg_match( '/^([adObis]):/', $data, $badions ) )
+	if ( ':' !== substr( $data, 1, 1 ) )
 		return false;
-	switch ( $badions[1] ) {
+	$badion = substr( $data, 0, 1 );
+	if ( !in_array( $badion, array( 'a', 'd', 'O', 'b', 'i', 's' ) ) )
+		return false;
+	switch ( $badion ) {
 		case 'a' :
 		case 'O' :
 		case 's' :
-			if ( preg_match( "/^{$badions[1]}:[0-9]+:.*[;}]\$/s", $data ) )
+			if ( preg_match( "/^{$badion}:[0-9]+:.*[;}]\$/s", $data ) )
 				return true;
 			break;
 		case 'b' :
 		case 'i' :
 		case 'd' :
-			if ( preg_match( "/^{$badions[1]}:[0-9.E-]+;\$/", $data ) )
+			if ( preg_match( "/^{$badion}:[0-9.E-]+;\$/", $data ) )
 				return true;
 			break;
 	}