I bought a skin and the client shows it took twice the amount even though it didn't? (Display issue)

(The basics of my issue) The top-right RP amount isn't the same as the amount I actually have. With the current Bonus RP event going on, I had just purchased 3000 Riot Points. I went to the shop and bought the newest Olaf skin, which is set at 750 RP. When I bought it, the RP counter at the top right of the client went from 3002 RP to 1502 RP. I thought it ate twice the amount of Riot Points, but when I went to double-check by clicking on the new Hecarim skin, it said that I have 2252 Riot Points. So the client didn't purchase the Olaf skin twice, but it displayed it in the top-right corner like it did. Does anyone know why that would happen? I have no actual issue of losing more RP than I should have, but this sort of thing has happened before.