The validation for Zero Width Joiners and other odd Unicode characters might need tweaking or implementing on user page edit validation.
Asking users one by one to change their name won't scale well if this is a bug in the validation code.
Here's what I see in comments about the lack of a linkable name:
Tearing into the rendering of the page, what would look like this for a user with a more traditional name:
<div class="user-details"> <a href="/users/5472/bmike">bmike</a><br> <span class="reputation-score" title="reputation score" dir="ptr">42</span> </div>
The user with the brief unicode name:
<div class="user-details"> <a href="/users/3936/">͏͏͏</a><br> <span class="reputation-score" title="reputation score" dir="ptr">42</span> </div>
Is this a bug in the user entry validation checks or the rendering of this particular name as it sits in the database or do I need to be equally clever to @ message users with names like this one on the site?