Muzzling works fine, when you unmuzzle however, you get an error: "Error to be mapped to message: Silence|UserNotMuzzled|BoA_SubZer0". Unmuzzling does not work right away.
If you reconnect, the muzzle itself is reset; however, it still says that the user is muzzled in the right click menu, and the error persists if you try to unmuzzle.
Thanks to Puma who notified me about this.
Update: It seems this applies to names containing zero, not just ending with it.
Another update: It seems to not be restricted to names containing zero. Just got a report where the muzzled user didn't have any special characters in his name; all letters and an underscore, like most people.