Vlad Mihalcea Could you make sure we get this documented in the guide where we talk about AttributeConverters? Something like:

In cases when the Java type specified for the "database side" of the conversion (the second AttributeConverter bind parameter) is not known Hibernate will fallback to serialization. Whether a Java type is "known" means whether it has an entry in the JavaTypeDescriptorRegistry. By default Hibernate loads many JDK types into the JavaTypeDescriptorRegistry. An application can also expand/alter the JavaTypeDescriptorRegistry. Adding a JavaTypeDescriptor to this registry means that we will know how to handle it at the JDBC level. <implications of serialization/>