unexpected use of TEMP ts in direct path insert of IOT

hi again folks

I am migrating 3.5 billion rows from an IOT hash partitioned to an IOT range partitioned.

The data and table layout remain the same.

As an alternative trial I ran the following - all names are only for demonstration

table_b is empty and all partitions have been pre-created for the data range in table_a

The reason for the order by was to indicate that the resulting data would be in the same order as the destination IOT

insert /*+ APPEND NOLOGGING */

into table_b

  (  pk_number_value,

     pk_timestamp_value,

     timestamp_value,

     number_value

  )

select /*+ PARALLEL(2) */

     a.pk_number_value,