Buying with IP

I recently got enough IP to get Taliyah (6403), but when I tried to purchase her it said I didn't have enough. so i logged back out and in again and was able to purchase her. Now, after playing a game with her, some how I have returned to 6403 IP, though the shop does recognize that i don't have enough IP to buy anything. After checking, this seems to apply to any purchase, not just champions. logging out fixes the total after a purchase, but once you buy something again your IP total freezes.