Encoded characters should be valid in mailto

Dear W3C validator,

We use a WordPress plug in that encodes mailto addresses to prevent showing
mailto in plain text in web pages.
Encoded characters should be valid in any html tags 'values'.

At the moment, we get the following HTML5 validation errors with Nu Markup
Checker:

   1.

   *Error*: Bad value mailto: webmaster@nsc.ca for attribute href on
   element a<http://www.w3.org/html/wg/drafts/html/master/single-page.html#the-a-element>:
   Illegal character in scheme data: not a URL code point.

   From line 162, column 59; to line 162, column 203

   s, e-mail *<a
   href="&#109;&#97;&#105;&#108;&#116;&#111;&#58;&#32;&#119;&#101;&#98;&#109;&#97;&#115;&#116;&#101;&#114;&#64;&#110;&#115;&#99;&#46;&#99;&#97;">*
   webmas
   Syntax of IRI reference:Any URL. For example: /hello, #canvas, or
   http://example.org/. Characters should be represented in
NFC<http://www.macchiato.com/unicode/nfc-faq>and spaces should be
escaped as
   %20.

Thank you

Best Regards

Daniel Servranckx
NSC Webmaster
web: http://nsc.ca

Mail to webmaster@nsc.ca <Webmaster@nsc.ca> is forwarded to Daniel
Servranckx, Catherine Gilbert and Hugh Morrin.