Unexpected output when bold and @user mixed using markdown_github

[mike-ward]

**@user** is converted to an email link using markdown_github

► pandoc -f markdown_github
**@user**
^Z
<p><script type="text/javascript">
<!--
h='&#x75;&#x73;&#x65;&#114;&#42;';a='&#64;';n='&#42;&#42;';e=n+a+h;
document.write('<a h'+'ref'+'="ma'+'ilto'+':'+e+'" clas'+'s="em' + 'ail">'+e+'<\/'+'a'+'>');
// -->
</script><noscript>&#42;&#42;&#32;&#x61;&#116;&#32;&#x75;&#x73;&#x65;&#114;&#42;</noscript>*</p>

► pandoc
**@user**
^Z
<p><strong><span class="citation">@user</span></strong></p>

Is this expected?

[jgm]

Hard case. GitHub markdown doesn't require <..> around
URLs and email addresses to turn them into links. And
**@user is actually a valid email address, though not
one you'd ever expect to see.

See
https://en.wikipedia.org/wiki/Email_address#Valid_email_addresses

A human can tell what's intended here, but it's unclear
what the rule should be that excludes interpreting this
as a bare email address.