On the other hand if you'd enter "ar" instead of Mark, you wouldn't find any Mark - why is that? More importantly why is it diacritics sensitive? Since there are many nationalities and not obvious characters (czech ones included) wouldn't be better to display everything regardless of carons etc.?
BTW - I realized many chat users can't be found by search. I guess it is because you can qwrite anything as a nickname, can't you? Since you are still guided to your match-league-country, is there any chance to see teams and not (just) nicknames. Or remove the option to type different nickname than your buzzerbeater one? It would be useful to know who are you talking to.