rest_v2/jobs MailNotification HTML Embedding Behavior Changed

We have been generating our reports using the rest_v2/jobs endpoint on JasperServer 6.1. We were passing:

outputFormats: { outputFormat: ['PDF', 'HTML'] }
...
mailNotification: {
  ...,
  resultSendType: "SEND_EMBED",
  ...
}

and it would attach the PDF to the email and embed the HTML within the email.

We upgraded to 6.4.0 and now the same request embeds the HTML in the email and attaches it (in addition to the PDF). This is causing issues with our accounting software. Was it an intentional change? I've found no reference to it in the changelogs or API docs. If not, is it something that's been reverted in later versions? If yes, is there any way we can return to the original behavior where the HTML report is embedded but not attached?

Thanks.