User format preference ignored when sending email

I tested this using the send email functionality that appears on the contact page on a site I run.

I used the three different email preferences (html, text and both) and added text in either the text both, plain box, or both. The results are listed below.

They were what you would expect apart from when I set my preference to plain text, added content in both the pain text and html box, but received content in html.

Presume this is controlled by a reasonably straightforward piece of logic somewhere (if only I knew where and am happy to submit a patch if you catch me on IRC/email and can point me to the right place.