The above was typed with all lines justified left, with plus signs at the beginning of lines 2 and 4 and minus signs at the beginning of lines 3, 5, and 6. Why the hell is Discourse changing what I type? There is NO excuse for this!
It is mis-interpreting your input as bullet points.
To get around it, enclose the whole thing in a preformatted text block. You can push the </> button in the toolbar, use the hotkey (CMD/CTRL-E), or enclose it with triple backticks (```) above and below.
The “txt” is optional, but lets Discourse know to not try to guess what’s in that block. Otherwise it might think it’s code of some sort and accidentally try to colorize it.
Discourse just tries to be too many things to too many people and will often mis-guess your input as something it wasn’t meant to be, especially if you start a paragraph with a symbol of any sort.