It appears that MAILMERGE fields within HYPERLINK fields are not updated like
MAILMERGE fields used elsewhere in a mail merge document as the merge is
being performed. Is this correct?

For instance, using the statement below within a document for Merge to Email
should, in theory, insert the value of the PONumber field for each record of
the data source into the mailto: hyperlink. If the HYPERLINK field is
manually updated using F9, the MERGEFIELD value is updated, the PONumber
value for the current record is incorporated into the hyperlink and the
hyperlink functions as expected, however, the MERGEFIELD value is not updated
when the Merge to Email sequences through each record.

{HYPERLINK "mailto "PONumber"}%20Already%20Paid" \o "Click here to send an email if you've
already paid"}

Is there a way to ensure that the MERGEFIELD within the HYPERLINK statement
is automatically updated when the Merge to Email sequences through the data
source records?

Thanks, Mark V