Two Markdown line breaks don't translate to a single line break in the output but to a paragraph break.
(To output a single line break, precede your source line break with two spaces. As others have pointed out, these behaviors are to let you manually wrap your source but have the output be auto-wrapped.)
> As others have pointed out, these behaviors are to let you manually wrap your source but have the output be auto-wrapped
Ah. That makes sense finally. However - I've never needed this ability whilst I constantly suffer from the non-intuitive default behaviour. Cure worse than disease?
(To output a single line break, precede your source line break with two spaces. As others have pointed out, these behaviors are to let you manually wrap your source but have the output be auto-wrapped.)