Well, I discovered it a while ago. I was trying to naming a rune page as Karma is a b*tch but the client warned me for using an offensive word on it. However, client does not warn you on masteries. It actually allows you to use offensive words on mastery pages.
[Rune page errors](http://i.imgur.com/wAdOJkx.png).
[Allowance on mastery page](http://i.imgur.com/uwqDVke.png).
Anyone has an idea?