Forum links to one of my user's profile page leads to the wrong url
 

The other admin of my site just noticed that when anyone clicks on her name to go to her user profile, it gives the following error: "An appropriate representation of the requested resource /index/member.php could not be found on this server."

The problem seems to be caused by the fact that her username, Wingéd Mermaid, has an e with an accent on it. The link it tries to go, which doesn't work, is:
http://mernetwork.com/index/member.p...ng%E9d-Mermaid

It substitutes the accented e with its unicode code point. I've found that if the accented e is replaced with a regular e, or with the UTF-8 representation of the accented e, then it goes to her profile:
http://mernetwork.com/index/member.php?2-Winged-Mermaid
http://mernetwork.com/index/member.p...C3%A9d-Mermaid


What I don't understand is why this suddenly started happening, and how to fix it.