The problem is that usernames are handled/converted internally to lowercase.

When you create a new user through the admin it gets converted to lowercase. But on registration it does not.

The fix is:

in /evocore/_usercache.class.php find

$this->cache_login[$Obj->login] = & $Obj;

(in method add()) and replace this line with

$this->cache_login[ strtolower($Obj->login) ] = & $Obj;

.

This will be fixed in the beta.

Thanks for the help blueyed.
That fixed it.