Just committed some line-height code that Johannes and I wrote.
When line-height is less than the font's ascent+descent, unhighlighting
gets confused. I think it has to do with using the line dimensions for
'area' for drawing the background. I'll dig into it a little more later on.
PS I see that firefox puts more space between its paragraphs than we do.
Their value seems to be related to the font size, or the default font size,
or something. Is there anything deep behind our use of 9?
