You need quotes for the href, either single or double.
Like this:
$title = urlencode($_POST['title']);
$issue = urlencode($_POST['issue']);
echo "<a href=\"http://www.mycomicshop.com/search?q={$title}+{$issue}&pubid=&PubRng=\">My Comic Shop</a>";
Also use urlencode() instead of htmlspecialchars().
Cheers.
Edited: Removed quotes added by CodeProject automatically.