Character encoding not being detected after upgrading to 38.2.0

[CB]

After upgrading I started to see strange character in some of my mails.

Examples:
estão
diretório

The message source has:
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable

If I change 'View > Character Encoding' from 'Western' to 'Unicode' the bad characters get fixed:
estão
diretório

But every time I change to another email, the Character encoding goes back to 'Western'

It looks like the message encoding not being detected automatically any more.

 $ lsb_release -rd
Description: Ubuntu 14.04.3 LTS
Release: 14.04

 $ apt-cache policy thunderbird
thunderbird:
  Installed: 1:38.2.0+build1-0ubuntu0.14.04.1
  Candidate: 1:38.2.0+build1-0ubuntu0.14.04.1
  Version table:
 *** 1:38.2.0+build1-0ubuntu0.14.04.1 0
        500 http://br.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu/ trusty-security/main amd64 Packages
        100 /var/lib/dpkg/status
     1:24.4.0+build1-0ubuntu1 0
        500 http://br.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.