It seems putting a '+' in there throws it. Maybe it's a markdown bug, or maybe the obfuscation markdown applies to email-links is being caught by the HTML sanitizer.
- -- [[JonDowland]]
+ -- [[users/Jon]]
+
+> It's a markdown bug. For some reason, markdown doesn't recognize the email with a '+' as an email:
+>
+> $ echo '<a+b@c.org>' | markdown
+> <p><a+b@c.org></p>
+>
+> htmlscrubber then (rightly) removes this unknown tag.
+>
+
+>> Filed [in CPAN](http://rt.cpan.org/Ticket/Display.html?id=37909)
+>> --[[Joey]] [[!tag done]]
+
+> But I've noticed some other Text::Markdown bugs that, even with htmlscrubber, produce
+> [ill-formed (X)HTML](http://validator.w3.org/check?uri=http%3A%2F%2Fikiwiki.info%2Fbugs%2Fmarkdown_bug%3A_email_escaping_and_plus_addresses%2F).
+> (View the markdown source of this page.)
+>
+> --Gabriel
+
+>> The htmlscrubber does not attempt to produce valid html from invalid. It
+>> attempts to prevent exploits in html. The tidy plugin can force html to
+>> valid. --[[Joey]]
+
+<tt>
+
+-
+>