From http://issues.fresco.org/bug35:

For some reason, every email I get from roundup
with a comment entered via the web form displays
in mutt like:

I've got it all designed and half implemented; ^M
just need to implement one more piece, and then^MI
don't know why -- I've never seen Mutt display a
message like that before.

I do know that control-M is the CR in DOS-style
CRLF line terminators, and I do know that roundup
is doing the slightly odd trick of sending mail with
  Content-Transfer-Encoding: quoted-printable
in the headers, and then coding all the ^M's as
the string "=0D", which is weird.

I have a guess: web browsers send form text back
with CRLF EOLs (I don't know this for sure),
Roundup doesn't realize this and interprets
messages the Unix way (LF EOLs), and quotes
messages the Unix way (CR as a special character).
 Then, the MTAs (which are supposed to handle EOL
conversion, I think?) don't notice the CR's
because of the quoting, and are unable to strip
them when delivering to my Unix machine.  (I don't
know what the messages come out like on Windows,
where they probably end up as CRCRLF.)

If this is the case, then Roundup just needs to be
taught that HTML forms may use CRLF line
terminators, and convert them appropriately... but
someone who knows more about these protocols is
welcome to correct me :-)