You have three lines in your first code block that contain several dozen trailing spaces each (and these spaces get wrapped by PM, which makes the "weird newlines").
I'll go out on a limb and guess that you are using Opera. Although I like a lot of things about Opera, it certainly has the most stupid bugs. This probably replaces the previous Opera bug where they'd add an extra blank line per non-blank line each time you preview.
Since this is affecting several people, it would be nice to track down the source and any work-arounds.