You probably don't realize this, but your note has the background defined as white, which for me means white text on white background. My default text is white, because my default background is dark gray.
So in your note, since the style of the background is defined by the HTML you pasted, I see white on white xD
Dianara 0.1-dev already has a "paste without formatting" option, but I doubt people would use that if they don't see anything wrong when pasting with the normal option.
JanKusanagi @i at 2013-08-12T13:11:22Z
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 :)