Doesn't Seem to Encode Linked Addresses

So, using a standard <a href="mailto:...">Joe Smith</a> link seems to bypass the system altogether. In looking at the documentation at http://recaptcha.net/apidocs/mailhide/ it seems that it's possible to do this, but whenever I enter a standard email link in this fashion it doesn't catch it... Instead, I have to enter it as the full email to get picked up by the recaptcha module.

Is it possible to add this additional level or am I missing something?

Thanks.