Update to 11.3-RC2 breaks SMART Reporting Script

After installing 11.3-RC2 the script reporting the SMART disk status was no longer being sent.
The error being reported :

Error: [EFAULT] Failed to send email: string payload expected: <class 'list'>

The sendmail header is being built like this :

Code:

1.  

   1.  

      1. Set email headers ###
         (
         echo "To: ${email}"
         echo "Subject: ${subject}"
         echo "Content-Type: text/html"
         echo "MIME-Version: 1.0"
         echo -e "\r\n"
         ) > "$logfile"

If I comment out the Content-Type line then the script works as it used to.
So something about Sendmail changed between 11.2 and 11.3