The oneboxing issue is fixed:
https://github.com/discourse/discourse/commit/0d62420cbe443b2cf1061405f83f34eef5103532
https://github.com/discourse/discourse/commit/0d62420cbe443b2cf1061405f83f34eef5103532
https://github.com/discourse/discourse/commit/0d62420cbe443b2cf1061405f83f34eef5103532
I did want to take a few moments to say 
to @Vitaly, it is absolutely amazing one can replace core behavior of the new engine in a very tidy and maintainable way without needing to fork the project. I am able to achieve in minutes stuff that used to take me hours when working with the previous Markdown engines.
The pipeline, date flow and token stream make for an amazingly clear design that is understandable by humans. Thank you.