Problems running a mixed groovy/java project

I have a project with both Java og Groovy classes. The editor treats everything properly, with auto complete, etc.

The project's JDK is an intelliJ SDK. The project is a plugin-project.

When I build the project, however, I get a parserproblem:

Error: cannot find symbol class ParseXmlmpl

The class throwing the compile error is a java class. The referenced class is the groovy class. Both classes are in the same package.

When I look in the "out" directory, there's no trace of the groovy class, so the compiler error is a proper error. How do I trigger the compile of the groovy class?!?