I\'m trying to display a bit of html in a message that\'s being displayed via the new Django messages framework. Specifically, I\'m doing this via the ModelAdmin.message_use
Have you tried {{ message | safe }}?
In the Django template system template variables are always escaped, unless you specify them as safe with the safe filter. This default makes even the unaware protected against an injection attack.
I'm not sure how that interacts with mark_safe, but perhaps something happened in between that made it unsafe again.