Well, in 1.0-dev you can edit the message after it's been posted. Not by editing the source HTML, but still...

If I copy your message and paste it into a new message, I also get the white background, but then using "Select All" and setting test to "normal" works for me.

Anyway, if you noticed something was wrong, that's good enough, because with 1.0 you could then undo and use the "paste without formatting" option :)