Dengue just reported this to me, so I'm going to combine his findings with two of my own and make one big ticket out of this.
Players can't be !rank'd by the Robo Refs if their name begins with "unt" (i.e. untie, Untame). I tried it myself — the bots return nothing and act as if the command is the furthest thing from their robotic minds.
Similarly, MatchBots ignore the !lag command when it's issued for a name beginning with "er" or "ger".
I'm pretty sure the server's list of obscene words is somehow interfering with the commands. When I try to PM myself the commands with the filter on, they don't go through. "rank unt" is kind of obvious, but I don't know why "lag er" and "lag ger" would be filtered.
Solution? That's for you to figure out, I'm just the messenger, heh.