This is an issue that was fixed via a pull request to the master branch of doctrine/dbal about 2 months ago. However, depending on the branch of Symfony 2 you are using, that doctrine/dbal fix may not be included.
https://github.com/doctrine/dbal/pull/373
If it is possible to use a version of Symfony 2 that includes this latest doctrine/dbal fix, I think you will see that issue go away.