Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 17302)
+++ wp-includes/functions.php	(working copy)
@@ -779,6 +779,9 @@
 function set_transient( $transient, $value, $expiration = 0 ) {
 	global $_wp_using_ext_object_cache;
 
+	if ( strlen( $transient ) > 45 )
+		return false;
+
 	$value = apply_filters( 'pre_set_transient_' . $transient, $value );
 
 	if ( $_wp_using_ext_object_cache ) {