Signup fails if server is not restarted after upgrade and restore

Signup fails with:

Cause: org.springframework.orm.hibernate.HibernateSystemException: a different object with the same identifier value was already associated with the session: 3, of class: com.opensymphony.user.provider.hibernate.entity.HibernateUser; nested exception is net.sf.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: 3, of class: com.opensymphony.user.provider.hibernate.entity.HibernateUser Stack Trace: [hide] org.springframework.orm.hibernate.HibernateSystemException: a different object with the same identifier value was already associated with the session: 3, of class: com.opensymphony.user.provider.hibernate.entity.HibernateUser; nested exception is net.sf.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: 3, of class: com.opensymphony.user.provider.hibernate.entity.HibernateUser net.sf.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: 3, of class: com.opensymphony.user.provider.hibernate.entity.HibernateUser at net.sf.hibernate.impl.SessionImpl.doSave(SessionImpl.java:823) at net.sf.hibernate.impl.SessionImpl.saveWithGeneratedIdentifier(SessionImpl.java:761) at net.sf.hibernate.impl.SessionImpl.save(SessionImpl.java:720) at org.springframework.orm.hibernate.HibernateTemplate$7.doInHibernate(HibernateTemplate.java:299) at org.springframework.orm.hibernate.HibernateTemplate.execute(HibernateTemplate.java:149) at org.springframework.orm.hibernate.HibernateTemplate.save(HibernateTemplate.java:297) at com.atlassian.confluence.user.persistence.dao.hibernate.ConfluenceUserDAO.saveUser(ConfluenceUserDAO.java:176) at com.opensymphony.user.provider.hibernate.HibernateCredentialsProvider.create(HibernateCredentialsProvider.java:64) at com.atlassian.confluence.user.providers.ConfluenceCredentialsProvider.create(ConfluenceCredentialsProvider.java:60) at com.opensymphony.user.UserManager.createEntity(UserManager.java:370) at com.opensymphony.user.UserManager.createUser(UserManager.java:242) at com.atlassian.confluence.user.DefaultUserAccessor.addUser(DefaultUserAccessor.java:59) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:324) at org.springframework.aop.framework.AopProxyUtils.invokeJoinpointUsingReflection(AopProxyUtils.java:59) at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:201) at