It's not actually the top border but a small shadow (so it's more
related to background rather than border).
To me this is a bug since
barckground:none;
should wipe it out, but it doesn't. A work around is to set a white
(or whatever) background image to the textarea:
background:#fff url(whitey.png);
border:0; margin:0; padding:0;
Note that something like the following also works:
background:#fff url(.);
But I don't like it at all.
Matt