Wrong content-transfer-encoding for e-mails via Mandrill on a Heroku hosted Play Framework 2 app. Works locally

I am using Heroku to host an app written in Play Framework 2.2.x (Java). Further, I am using Mandrill by Mailchimp to automatically send e-mails.

In my local environment, I can send e-mails via Mandrill and everything looks fine. According to GMail the e-mails have the following encoding:

MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable

However, when deploying to Heroku and doing the same, the e-mails look garbled. According to GMail, the e-mails now have the following encoding:

MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit

The site itself on Heroku looks fine and displays exotic characters in UTF8 without any problems.

I should mention that I am using templates and play-easymail (https://github.com/joscha/play-easymail/) to generate e-mails: that is, I populate the body of an e-mail with the string views.html.emails.myEmailTemplate.render().toString().