Bags (the corresponding Java type is List), as they can contain non-unique elements. The reason is that persisting, for example a bag of String-s, violates a principle of relational databases: that each table is a set of tuples. In case of bags, however (which require a join table), if there is a duplicate element, the two tuples corresponding to the elements will be the same. Hibernate allows this, however Envers (or more precisely: the database connector) will throw an exception when trying to persist two identical elements, because of a unique constraint violation.

There are at least two ways out if you need bag semantics:

When a collection is mapped using these two annotations, Hibernate doesn't generate a join table. Envers, however, has to do this, so that when you read the revisions in which the related entity has changed, you don't get false results.

To be able to name the additional join table, there is a special annotation: @AuditJoinTable, which has similar semantics to JPA's @JoinTable.

One special case are relations mapped with @OneToMany+@JoinColumn on the one side, and @ManyToOne+@JoinColumn(insertable=false, updatable=false) on the many side. Such relations are in fact bidirectional, but the owning side is the collection (see alse here).

To properly audit such relations with Envers, you can use the @AuditMappedBy annotation. It enables you to specify the reverse property (using the mappedBy element). In case of indexed collections, the index column must also be mapped in the referenced entity (using @Column(insertable=false, updatable=false), and specified using positionMappedBy. This annotation will affect only the way Envers works. Please note that the annotation is experimental and may change in the future.