I tried to do a one-to-many mapping where the "one" side was a Groovy domain class and the many side was a JPA annotated class (You know an EJB3 entity bean). And it failed. Oh, the misery and woe! Well, okay it's not quite that bad.
So the lesson learned children? Don't do drugs, stay in school, use JPA or use GORM, be careful using both. I have filed this bug hoping that next time the stogy is a fine cuban cigar: GRAILS-1983. Bender likes fine cigars.