I have just added a posting in this forum, with C# code. The code doesn't look very nice, but it has correct line breaks and colouring (still with proportional font). Then I edited the post to add something to the end. After that, the post's code section
had many additional line breaks and more gaps everywhere. Pretty ugly now. I'm sure somebody will reply that it's broken and how I should have done it (which I did, originally).
Here's the post: http://social.msdn.microsoft.com/Forums/en-US/winforms/thread/4aaa998b-cdcb-4581-8255-cb1d6a164536 (2nd reply, there's no direct link or absolute time stamp)
Browser: Firefox 4.0 RC1 on Windows 7 x64.
Have you ever thought about using vBulletin or another professional-grade and well-tested forum software? This thing here works pretty unexpected, always had loads of weird bugs and is still sloooow as hell (10+ seconds for the front page)!