[Users] Not displaying HTML email automatically (sometimes)

[Jerry]

claws-mail version 3.14.0

System Information
GTK+ 2.24.30 / GLib 2.49.2
Locale: en_US (charset: ISO-8859-1)
Operating System: Win32

I am running claws-mail on a Windows 10 PRO amd/64 bit machine.

After updating, several, although not all HTML messages are being
displayed as plain text. I cannot figure out why this is happening.

An example of one that does not display properly now but use to has the
following headers:

Content-Type: text/html
Content-Transfer-Encoding: 7bit

Messages with this header usually display properly:

Content-Type: text/html; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable

None of the settings have been changes and I have set all of the
defaults to display the HTML part first if it is present.

Also, and I don't know if it is related, meeting requests that are used
in vcalendar now always start out in plain text. This is not how it use
to work. This is an example of one header:

MIME-Version: 1.0
Content-Type: text/calendar; method=REQUEST;
	charset="utf-8"
Content-Transfer-Encoding: 7bit
X-Mailer: Microsoft Outlook 16.0
Thread-Index: AdHGQLkv/uf1u5B4Sp2rfa9Y4tpbHQAAHn/wAAALpoA=
Content-Language: en-us

I would be happy to supply examples if required.

-- 
Jerry