Barbara,
What you are describing is an Account Setting (under ACCOUNT SETTINGS > COMPOSE > REPLY HEADER TYPE). If this setting is set to "Full" it will display the entire Header upon Reply. If it is set to "Basic" it would only display From:, Sent:(Date/Time), To:, and Subject: fields.
You would want to make sure that "Reply Header Type: Basic" is set as the User Default under SETTINGS > DEFAULTS > USER DEFAULTS > COMPOSE. You can then use USER PROPAGATION to change all users back to Basic if had been set to Full previously.