Exemplos:
https://forum.monocycle.info/search?q=%40MouvementOndulatoireUnifié
https://forum.monocycle.info/search?q=%40Aurélien
Pesquisar com nomes de usuário sem caracteres especiais funciona:
https://forum.monocycle.info/search?q=%40canapin
https://forum.monocycle.info/search?q=%40bouin-bouin
Estou usando o Discourse 2.9.0.beta9 (c245b74398)