As this issue confused me, I took a look into it and the reason seems to be that there's no current release of doctrine/orm including this bugfix. It's not part of the current v2.4.2 tag:
We'd be really happy to get a new bugfix release.
Running those lib versions:
doctrine/annotations v1.1.2 Docblock Annotations Parser
doctrine/cache v1.3.0 Caching library offering an object-oriented API for many cache b...
doctrine/collections v1.2 Collections Abstraction library
doctrine/common v2.4.2 Common Library for Doctrine projects
doctrine/data-fixtures v1.0.0 Data Fixtures for all Doctrine Object Managers
doctrine/dbal v2.4.2 Database Abstraction Layer
doctrine/doctrine-bundle v1.2.0 Symfony DoctrineBundle
doctrine/doctrine-fixtures-bundle v2.2.0 Symfony DoctrineFixturesBundle
doctrine/inflector v1.0 Common String Manipulations with regard to casing and singular/p...
doctrine/lexer v1.0 Base library for a lexer that can be used in Top-Down, Recursive...
doctrine/orm v2.4.2 Object-Relational-Mapper for PHP