Every time I get into champion select with a champion I own multiple skins for, any skin that I did not last use gets selected at random.
Nothing game-breaking, just thought I'd put it out there.
How to reproduce:
Go into champion select.
How often does it occur:
Every time as long as the prerequisites described are met.
Short note: This may or may not happen to everyone. I have confirmed with three friends who have the same issue so far.