This is thanks to a fabulous pull request by Yixuan Qiu who single-handedly managed to upgrade to the new minor release of Eigen -- after having expanded the unit tests a few weeks earlier in another pull request.
NEWS file entry follows.
Changes in RcppEigen version 0.3.2.3.0 (2014-12-22)
Updated to version 3.2.3 of Eigen
Added a number of additional unit tests for
Updated one of the examples