I am not too familiar with the core structure and intent of the envers code base but stepping through the code has left me with the following comments.

org.hibernate.envers.event.spi.BaseEnversCollectionEventListener
In the method protected final void onCollectionAction(...) there is a check for the RelationDescription to determine if it is not a "fake" many-to-one bidrectional relation. However, there seems to be a mismatch for property metadata separators used. dot "." vs underscore "_".

			// Checking if this is not a "fake" many-to-one bidirectional relation. The relation description may be
			// null in case of collections of non-entities.
			final RelationDescription rd = searchForRelationDescription( entityName, referencingPropertyName );

			// We could adjust the stored key here as a work around.
			// final RelationDescription rd = searchForRelationDescription( entityName, referencingPropertyName.replace('.',  '_') );

Resolving this issue in the manner suggested above now leaves with no error on persisting, but the position column and the foreign key in ENVERS_ITEM_AUD back to ENVERS_HEADER_AUD are left null in the audited tables.

org.hibernate.envers.configuration.ClassesAuditingData
Given the above work around, the next issue seems to fall in updateCalculatedFields().