Event Rewards

I've been doing the missions slowly and was saving up the currency tokens in order to get a reward. I logged in yesterday and found that the rewards page had all changed to the new event (popstar whatever) and all the old rewards are gone, but the new rewards page uses the same currency.

Why do 2 different events use the same currency? Kind of feels bad as I finally saved up enough to get the Halloween themed reward while the Halloween missions were still available but then the currency I earned with those missions is carried over into the next event.

In previous events when there were 2 events back to back they had different currency, and as long as your first currency didn't expire you could still purchase the rewards. Really lame....