Why does Apache CXF throw IllegalAnnotationsException when I add reference to other beans?

I have 2 Web service classes that I mean to expose as SOAP services using Apache CXF. One of the services refers to the other as part of its operations. I have set up Apache CXF into my Grails app (no plugins), and set up my Web services through resources.groovy (Spring Bean DSL).

Say I have the following classes:

@WebService
BookService {
    //class definition
}

and:

@WebService
LibraryService {
    BookService bookService
    //class definition
}

I declare them in my resources.groovy as follows (namespace declarations omitted):

bookService(BookService)
jaxws.endpoint(id: 'bookService', implementor: "#bookService", 
        address: '/book')

libraryService(LibraryService) {
    bookService = ref('bookService')
}
jaxws.endpoint(id: 'libraryService', implementor: "#libraryService", 
        address: '/library')

However, every time I run my app (via grails run-app) I get IllegalAnnotationsException:

Caused by IllegalAnnotationsException: 2 counts of IllegalAnnotationExceptions
->> 106 | check    in com.sun.xml.bind.v2.runtime.IllegalAnnotationsException$Builder

and I don't understand why its occurring. I'm new to Apache CXF so I hope someone can enlighten me on this.