Enhancer yields "does not have a public no-args constructor." exception for entity with protected qualified constructor

Entity with protected qualified constructor:

@Entity
public class Kunde {
....
protected Kunde()

....
}

causes enhancer to fail with message like:

C:\>wsenhancer test\Kun*.class
82 ConstructorDemoWeb INFO [main] openjpa.Tool - Enhancer running on type "class at.arz.domain.core.Kunde".
Exception in thread "main" <openjpa-2.2.3-SNAPSHOT-r422266:1485013 fatal user error> org.apache.openjpa.util.MetaDataException: The id class "class test.Kundennummer"
specified by type "class test.Kunde" does not have a public no-args constructor.
at org.apache.openjpa.meta.ClassMetaData.validateAppIdClassMethods(ClassMetaData.java:2161)
at org.apache.openjpa.meta.ClassMetaData.validateAppIdClass(ClassMetaData.java:2067)
at org.apache.openjpa.meta.ClassMetaData.validateIdentity(ClassMetaData.java:2034)
at org.apache.openjpa.meta.ClassMetaData.validateMeta(ClassMetaData.java:1946)
at org.apache.openjpa.meta.ClassMetaData.resolve(ClassMetaData.java:1807)
at org.apache.openjpa.meta.MetaDataRepository.processBuffer(MetaDataRepository.java:828)
at org.apache.openjpa.meta.MetaDataRepository.resolveMeta(MetaDataRepository.java:725)
at org.apache.openjpa.meta.MetaDataRepository.resolve(MetaDataRepository.java:649)
at org.apache.openjpa.meta.MetaDataRepository.getMetaDataInternal(MetaDataRepository.java:417)
at org.apache.openjpa.meta.MetaDataRepository.getMetaData(MetaDataRepository.java:388)
at org.apache.openjpa.enhance.PCEnhancer.<init>(PCEnhancer.java:286)
at org.apache.openjpa.enhance.PCEnhancer.run(PCEnhancer.java:4885)
at org.apache.openjpa.enhance.PCEnhancer.run(PCEnhancer.java:4831)
at org.apache.openjpa.enhance.PCEnhancer$1.run(PCEnhancer.java:4801)
at org.apache.openjpa.lib.conf.Configurations.launchRunnable(Configurations.java:761)
at org.apache.openjpa.lib.conf.Configurations.runAgainstAllAnchors(Configurations.java:751)
at org.apache.openjpa.enhance.PCEnhancer.run(PCEnhancer.java:4796)
at org.apache.openjpa.enhance.PCEnhancer.main(PCEnhancer.java:4787)
Caused by: java.lang.NoSuchMethodException: test.Kundennummer.<init>()
at java.lang.Class.throwNoSuchMethodException(Class.java:327)
at java.lang.Class.getConstructor(Class.java:354)
at org.apache.openjpa.meta.ClassMetaData.validateAppIdClassMethods(ClassMetaData.java:2159)
... 17 more