The Discourse editor supports Markdown, BBCode, and HTML, but it also sometimes picks up invisible formatting when I cut and paste from other sites or software into the editor.
For example, if I copy one of my posts from Chowhound and paste it here, the text is indented and has a bunch of line breaks. I tried wrapping the paragraphs in HTML paragraph tags to fix that, but it had no effect.
If I paste into a text editor first and then copy and paste into the Discourse editor, everything’s clean, no line breaks, normal spacing between paragraphs.