I can't believe they haven't fixed this and your message is FIVE YEARS OLD. I just wrote a long reply on a message board and hit "preview" and it's all smushed together - it looks like none of my returns went through. So I googled my problem and came up with your post. It sounds like you're saying that if I actually post the message it will be formatted the way I had it.
What's the point of "Preview" if it doesn't actually preview the formatted message?
It seems like somebody at Ancestry.com wrote the programming code for the message board system like eight years ago and just dropped it. If anyone at Ancestry.com is reading this, please fix.