How do you fix quoting so that ruby-forum.com is happy?

I'm subscribed to this Google Group through email and reply to messages through Thunderbird but many of the messages I quote have the quoted part truncated or otherwise messed up when displayed in ruby-forum.com, which is where I actually read the messages. Is there a way I can "adjust" the quoting by Thunderbird so that doesn't happen? The quoted part shows up fine in Thunderbird and in Google Groups so there's something specific to Ruby Forum that it doesn't like.

Hey Michael,

this might be the problem with your thunder-bird settings, check
what's the outgoing email content-type
Try changing that, with some test mails. (It may be either in
preference dialog or your account setting).

Good Luck,