I figured it out. There is a Mac profile in parent pom that add '-d32', hence it enforces 32-bit compilation.
Shouldn't that vm-arg be removed?
We added that argument because it speeds up compiles significantly on Mac JDK 6. Apparently it's not compatible with Oracle JDK 7. Probably the best thing to do would be for us to refine the profile activation rules so it only applies when (OS=Mac and JDK=1.6). If you've made a change like this that's working for you, we'd love if you could send us a pull request!