EDIT

I created a new name which is having Achnantheiopsis boreolanceolata Lange-Bert. as basionym. I opened this name in the TaxonNamePopupEditor added the existing name 'A. Braun' as basionym author. Saving the name caused a PermissionDeniedException:

Caused by: eu.etaxonomy.cdm.database.PermissionDeniedException: [UPDATE] not permitted for 'andreas' on Person[uuid:c2efe190-b59c-4ce2-ae71-a1435347ac6c', toString:'Lange-Bert.']
    at eu.etaxonomy.cdm.persistence.hibernate.CdmSecurityHibernateInterceptor.checkPermissions(CdmSecurityHibernateInterceptor.java:196)
    at eu.etaxonomy.cdm.persistence.hibernate.CdmSecurityHibernateInterceptor.onFlushDirty(CdmSecurityHibernateInterceptor.java:124)
    at org.hibernate.event.internal.DefaultFlushEntityEventListener.invokeInterceptor(DefaultFlushEntityEventListener.java:348)
    at org.hibernate.event.internal.DefaultFlushEntityEventListener.handleInterception(DefaultFlushEntityEventListener.java:325)
    at org.hibernate.event.internal.DefaultFlushEntityEventListener.scheduleUpdate(DefaultFlushEntityEventListener.java:276)
    at org.hibernate.event.internal.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:143)
    at org.hibernate.event.internal.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:216)
    at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:85)
    at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:38)
    at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1282)
    at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:465)
    at org.hibernate.internal.SessionImpl.flushBeforeTransactionCompletion(SessionImpl.java:2963)
    at org.hibernate.internal.SessionImpl.beforeTransactionCompletion(SessionImpl.java:2339)
    at org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl.beforeTransactionCompletion(JdbcCoordinatorImpl.java:485)
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.beforeCompletionCallback(JdbcResourceLocalTransactionCoordinatorImpl.java:147)
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.access$100(JdbcResourceLocalTransactionCoordinatorImpl.java:38)
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl$TransactionDriverControlImpl.commit(JdbcResourceLocalTransactionCoordinatorImpl.java:231)
    at org.hibernate.engine.transaction.internal.TransactionImpl.commit(TransactionImpl.java:65)
    at org.springframework.orm.hibernate5.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:581)
    ... 113 more

This seems quite strange that the author of the basionym is being changed when adding basionym author to the name

Adding the basionym to the name with existing basionym author is not causing this problem, but it occurs when removing the basionym author afterwards.

But the same happens with the combinationAuthors.

There no such problem with the ex-basionym author, though.