Adding User to newly created group throws exception

I used the new alpha8 admin tool to create a new user (lht) and a new group (admin). When I assigned the user to the admin-group, I got the exception below. But after reloading, the assignment is displayed correctly. I am using h2 db.

can you reproduce it?

stacktrace:
13:33:55,014 WARNING [ExceptionHandler] (http-/127.0.0.1:8080-2) org.camunda.bpm.engine.rest.exception.InvalidRequestException: Exception adding user to group admin:

1. 1. 1. Error updating database. Cause: org.h2.jdbc.JdbcSQLException: Unique index or primary key violation: "PRIMARY_KEY_E ON PUBLIC.ACT_ID_MEMBERSHIP(USER_ID_, GROUP_ID_)"; SQL statement:
         insert into ACT_ID_MEMBERSHIP (USER_ID_, GROUP_ID_)
         values (
         ?,
         ?
         ) [23505-168]
      2. The error may involve org.camunda.bpm.engine.impl.persistence.entity.MembershipRelation.insertMembership-Inline
      3. The error occurred while setting parameters
      4. SQL: insert into ACT_ID_MEMBERSHIP (USER_ID_, GROUP_ID_) values ( ?, ? )
      5. Cause: org.h2.jdbc.JdbcSQLException: Unique index or primary key violation: "PRIMARY_KEY_E ON PUBLIC.ACT_ID_MEMBERSHIP(USER_ID_, GROUP_ID_)"; SQL statement:
         insert into ACT_ID_MEMBERSHIP (USER_ID_, GROUP_ID_)
         values (
         ?,
         ?
         ) [23505-168]
         at org.camunda.bpm.engine.rest.sub.identity.impl.GroupMembersResourceImpl.createGroupMember(GroupMembersResourceImpl.java:38)
         at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
         at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
         at java.lang.reflect.Method.invoke(Method.java:601)
         at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:167)
         at org.jboss.resteasy.core.ResourceMethod.invokeOnTarget(ResourceMethod.java:269)