Serendipity 1.4.1 has been released. This is mainly a bugfix release for the updated of the bundled Smarty library, which fixes issues with Serendipity 1.4.
Other small fixes include better antispam checks for pingbacks (they were too strict before), an update to the sql index key creation of the statistics plugin and removal of error messages on open_basedir enabled servers.
You only need to upgrade to Serendipity 1.4.1 if one of the mentioned bugs affect you. Updating is easy and documented online.