Then what about adding some feature like Bancho messaging you all the data, and then you get there a link to send a complaint in case you do not agree with the mute reason. Of course using this to report dumb stuff/spam would be punished. That's applied in many games/chat systems and it's kind of logic, like I'm not going to come here to the forum 2 days after I got random-muted and PM you wasting your time reading my message and finding out what happened. It's pretty much to add some system like the cheater's report one. Then again with this you/whoever reads it would get a message with all the necessary information, which will be even more accurate than any information biased you can get from a user.
I don't really use any osu!'s chat channel because of this, and I'm not the only one. If you want an specific case, a long time ago lots of players from Argentina had to create a private chat room somewhere else because of how retarded mods were on #spanish, just saying this so you know this is NOT some random issue happening now and then, or just to me. :p