I guess you're talking about
this post. Text wrapping is turned off inside [code] tags, as you'd expect. If one line is really long inside [code] tags though, that will essentially force the whole screen to be wide enough for that line (creating a scrollbar if necessary). Outside the [code] tags, all the line-wrapped lines will use the same ooverall screen width - so they will also be really long. So the solution is to be careful not to have really long lines inside [code] tags.
Note that you can edit your own posts after you've posted them, to fix this problem. Just look for the little pencil-and-paper icon at the top of your post, left of the quote "" marks icon.