[CLIENT] View other players' Masteries, and which S Chests they have received
All right, so you know how if you search a friends' name in the client, it will have the "Champions" and "Item Sets" tabs greyed out?
Well, if you put in their name, hit enter, click the "view/edit your summoner profile" button (The headshot between help and hextech crafting) as soon as possible, and then click "Champions" ONCE as soon as it's available, you will get to see their masteries, as well as which champions they have gotten S-rank chests on. The curious thing about this is it will still show your own list of which champions are unlocked.
Screenshots of a friend of mines' list as an example:
As seen, among other things, he has a mastery 7 Syndra with S chest, whereas I don't even own Syndra.
Not really a "major" bug as far as I know, but a neat little feature.