This happens to me on PBE if I am upgrading units. E.g. if I have 2 Vaynes on my bench and want to buy a third to Upgrade it to Level 2, I still pay for 3 Vaynes although I already payed for two units the rounds before. This is really annoying as it destroys your savings..
It happened twice in my game today. I upgraded a Nidalee on my bench from level 1 to level 2, and when I bought the 3rd Nidalee, it charged me 3 gold instead of 1. It also happened in the same game with a Warwick I bought. I did have a level 2 Warwick and Nidalee in the field at the time that I upgraded the champions on the bench.
Update: Also happened when I upgraded a Katarina on my bench to level 2, except it wiped out my remaining gold, it was greater than 5, but less than 10.
Update: It's happening to me on live servers (EUW) as well now.. Unplayable tbh..
