I'm not sure if this is or not useful, but I would be interested in knowing which files are the names failing for. i.e: do the same search using another client without the bug, and tell us which characters are the ones failing, I had the same issue using Fedora Core 2, wx2.4.3 no unicode, and aMule RC7, but I think the problem is Fedora's, not aMule's, since unicode seems broken in many other apps (notoriously firefox and eclipse)
Regards.