BuddyPress.org

@mercime, I haven’t pinpointed the exact piece of code that triggers it to do this. This is not just an issue with the buddypress forums as other forum software have this issue also, thats why most of them have syntax highlighting for code whenever the code tags are inserted, as syntax highlighting safely puts code inside of the highlight, as of without it, the webpage will attempt to apply that piece of code inserted into the layout of the page. Same with CSS. Occasionally, there is something that clashes with both, so you get the screwed up layout. Example of adding CSS directly to page via code no syntax

Why does it do this? I have no clue!