See: http://www.symfony-project.org/blog/2008/05/09/symfony-1-0-15-is-out
After the release of PHP 5.2.6 here is symfony 1.0.15. This revision fixes a regression in php5.2.6 and we do recommend you to upgrade if you plan to upgrade your PHP. Symfony 1.1 is not impacted by this problem.
Nice turnaround by the Symfony devs! Makes you wonder about the PHP team’s quality control, though..