RadioPublic Player Onebox

I’m trying to embed podcast players from RadioPublic. Posting a link only gets me a standard onebox:

But RadioPublic claim that they use oEmbed. I have inline onebox on all domains enabled and I have also whitelisted for iframes.
Using embed codes from RadioPublic works fine and embeds players correctly, but it would be much easier for users to just use the URLs.
Is this a Discourse issue at all or should I approach RadioPublic about this?

I stumbled upon this discussion

and now I’m wondering if the problem with the RadioPublic player is similar? Can you do the same thing for RadioPublic, @nbianca ?
Edit: It works, but not in the post preview. Only when I publish the post, the player appears.
Edit 2: After further research, it turns out that Stitcher links also don’t work, even though they do on iframely.
Soundcloud links also don’t show the player in post preview.