I don’t have any non-default onebox settings:
It looks like some shorts work on my site, but not all. For example, @nat’s ‘The Twins’ short gets embedded properly, but @Shauny’s does not.
And, not sure if this is relevant, but another difference I noticed between them is that Natalie’s shows a picture in the WYSIWYG preview and Shaun’s does not:
That seems to be consistent for other shorts that do and don’t embed properly on my site.
Shaun, can you replicate?