Oracle schedule job email notification question

I get incorrect email content from the Oracle (11gR2) schedule job email notification:

The email notification has shows incorrect value for the part of the "Subject".
SYS_CONTEXT('USERENV','SERVER_HOST') -- this part should shows another server name.

I separately tested:
select sys_context('userenv','server_host') from dual;
On the server and using the same user and I get the correct output (correct server name).

If I re-create a new job and add the email notification (via the same attached code) I get the correct "Subject".

In case the sys_context('userenv') parameter was changed since the scheduled job was created -- the scheduled job will show the old parameter value. I guess I could fix this by dropping and recreating the scheduled job. But that will erase the job history -- I guess so -- if, so that is not a choice.

Otherwise how can I let it show the correct server name in the current job itself....
thanks!

BEGIN
DBMS_SCHEDULER.ADD_JOB_EMAIL_NOTIFICATION (
    job_name   => 'MY_JOB',
    recipients => 'me@yahoo.com',
    sender     => 'me@yahoo.com',
    events     => 'job_failed',
    subject    => 'My Job Failed: %job_owner%.%job_name%'||' - '||SYS_CONTEXT('USERENV','SERVER_HOST'),
    body       => 'Job Failed: %job_owner%.%job_name% Event: %event_type% Date: %event_timestamp% Error code: %error_code% Error message: %error_message%'
  );

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