When fill-paragraph is applied to
;; - This is a long line that will wrap when it is filled.
it is filled like this
;; - This is a long line that will wrap when it is
;; - filled.
I do not understand why there is a "-" char on the second line
above. I would expect that it looked like
;; - This is a long line that will wrap when it is
;; filled.
It's a limitation of the current adaptive-fill-mode code.
It actually works in my local Emacs implementation, because I've added
various hacks to it, but this is post-22.