Masteries Mysteries?

so there i was, playing league of legends with my pals during the game, my friend EPICM0M0 was complaining about how her masteries were wrong, due to her inability to perform up to her usual standards we lost that game... But the exciting part comes now. while setting up for the next game, in champion select (since we adore your game), she noticed something was off. that's when she mentioned the words that rang a bell in my mind, somehow my masteries were appearing as hers. she sent me images, and there was no doubt about it my varus, ashe and nami mid masteries were all replacing her once jg main masteries. it was devastating so riot, what do you have to say about this bug that made me feel very exposed all in all, this situation is peculiar and bizarre, please fix it sincerely, mimzy111