Oracle MERGE (upsert) ; unusual increment of SEQ val even when match found

Question

I'm using Oracle Merge to do an UPSERT. It looked to be working fine until i noticed my SEQ is always incremented by 1 even when the when matched then side of the equation is satisfied. I know that the update side of the equation is being called because the status is updating as required (the name is a primary key so this wouldn't work purely by re-inserting the row). I've included my procedure below. Any ideas why this is happening?

CREATE OR REPLACE PROCEDURE ff_update(argname  VARCHAR,
                                      argstate VARCHAR)
AS
  BEGIN

    MERGE INTO flags f
    USING (SELECT argname name FROM dual) b ON (f.name = b.name)
    WHEN MATCHED THEN
                UPDATE SET f.state = argstate
    WHEN NOT MATCHED THEN
                INSERT (f.id, f.name, f.state, f.notes1, f.notes2)
                VALUES (id_seq.nextval, argname, argstate, NULL, NULL);

  END ff_update;
  /

And the sequence

create sequence ID_SEQ
start with 1000000
increment by 1
nocache;

Answer 1

This is expected behaviour for MERGE.

See Metalink Note: 554656.1 "Merge Increments SEQUENCE.NEXTVAL for Both Insert and Update"