Just making sure people are aware this happened so they can fix quickly:
In the latest release, it looks like Marketo pushed a change in Field Management so there is now a "HTML Encode Tokens in Emails" checkbox. When this rolled out, all fields defaulted to CHECKED.
As a result, the text area field we were using to populate dynamic rich text in our email footer was encoded HTML, causing it to show up as though it were plain text:
I'm guessing this is a security improvement intended to help neutralize code injection - but it would have been nice if this had been mentioned in the release notes...
I recommend other users audit what fields they are using in this fashion and make sure this is unchecked in Admin > Field Management.