[wp-hackers] Weird behaviour with comment_author_url and input placeholders

[Lynne Pope]

I've been working on two sites, one on WP 2.9.2 and another running 3.0.4.
Both require their comment forms to be written in HTML5 using the
placeholder tag.

eg.
 <label for="url">Website</label>
<input type="url" name="url" id="url" value="<?php echo
esc_attr($comment_author_url); ?>" placeholder="Enter Website Address
(optional)" pattern="https?://.+">

In testing, we have identified a problem with comment_author_url that occurs
when people do not input an URL. For some reason, WordPress is picking up
the placeholder text and saving it into the database, like so:
http://EnterWebsiteAddress(optional)

I'm having real trouble trying to identify why this is happening. The
placeholder attribute isn't inside the input value so should not be getting
picked up.

Is this a bug? I realise HTML5 placeholder attributes are still reasonably
new but it's not hard to have this working across current browsers so I
suspect others will hit the same issue.

Cheers,
Lynne