Nice masteries bro, let me borrow those

Not sure if this has been reported yet, however you can "steal" someone's mastery pages.

I was sitting in champ select (Team builder) and screwing around waiting for a role to fill, I went to my friends profile and was going through their mastery pages. Heard the noise of someone joining the game and hit the "home" key under the timer and returned to the lobby, but I noticed my mastery page had a new name. So I pressed the drop down and not only was one page taken, but every single one of them.

Lately I've only been running 3-4 mastery pages (thunderlords, amirite) however it takes any and all mastery pages they have. Usually not a big deal, but it's not fun to start the game as a marksman with tanky support masteries or the like.

This wasn't a one off blip either, I can repeat it over and over with any summoner (Even myself to the fix the error if necessary)