I noticed that other clients may not.

I'm thinking that consistency is more important here, long form text should be treated as markdown but I think normal posts should not.

I think this is a bug not a feature.

> 1: text_note: the content is set to the plaintext content of a note (anything the user wants to say). Content that must be parsed, such as Markdown and HTML, should not be used. Clients should also not parse content as those.

https://github.com/nostr-protocol/nips/blob/master/01.md

(Although It is nice to have rich content... 🤷🏻)