I notice that the (x)html code used with a valid (x)html icon on the validation results page of the validator is different from that specified on the validator's help page   (http://validator.w3.org/docs/help.html)

On the results page the (x)html code is:

        <a href="http://validator.w3.org/check?uri=referer"> ... </a>

while the (x)html code on the help pages is:

        <a href="http://validator.w3.org/check/referer"> ... </a>

My experience is that the former doesn't work as I expected while the latter does.  The check?uri=referer version sends me to http://validator.w3.org/ while the check/referer version causes the validator to validate my page.  This second is what I expected.  Simply reading check?uri=referer in the link it would seem that the link would cause the refering page to be validated.  That appears to not be true.  I've tried this with two browsers and get the same results so it appears to me that the check?uri=referer link is not doing what it should be.

It would seem to me that since there are at least these two possibilities, the help page and the results pages should include some sort of descriptive text like this:
... Here is the HTML you could use to add this icon to your Web page:

To link to the validator's home page use:
  <p>
    <a href="http://validator.w3.org/"> ... </a>
  </p>

To use the link to revalidate the Web page it is in, use:
    <p>
      <a href="http://validator.w3.org/check/referer"> ... </a>
    </p>