@bryan
Not just mastodon, but Fediverse wide: inconsistent markdown (or html) support amongst the various platforms... or even amongst the same platform, the _clients_. <- while mastodon supports markdown, some masto clients will render that as italicized, others wont. My client, #phanpy WON'T, but it has no problem with "code" `like this` oddly.
The body or `content` field of a Note object in the ActivityStreams parlance is presented as-is, up to the recipient to render how they like. SO try a different client
Im writing an ActivityPub server myself, and I make the assumption that `content` of a Note object may contain markdown - so anytime I render it, any markdown gets .. marked up accordingly. But that may break on a user who enters `# foo` into that field, because i'm going to render that as an `.h1` in my html interface.. when all they wanted was a pound/hash symbol. So then, do I then look for an "escape" character like `\# foo`?. It gets complicated.