I don't get it... I just had enough to use one Overdrive, one Note Power Up, and one Track Power-Up in a song. This was over 750 coins. I finish the track, pick a different one, and I notice that the items I had bought are no longer equipped. I try to re-equip them, and it tells me I don't have enough, that I only have 625. So what happened to the rest of the money I had and the money I supposedly earned on the last track?