So is that what happened to me? I was at 6200 IP for making 6 payments on my Brew Master tier and making separate purchase of a Villager Token and Guild Token. When the website last updated, my IP went to 6300 to reflect two people using my friend code to register and purchase the game. It also gave me $10 in-store credit. When I went to make another payment on my Brew Master tier, the payment system automatically included my $10 in-store credit (was going to save it to buy bonus EP, but since it is all going towards the same things, I didn't worry about it). Once the payment went through, my IP was 7200. Was the extra 100 IP from my friends only temporary because it was reflecting in-store credit?
Edit: You know what. Using "math" and "logic" to think about it. I only paid $90 of my own money which, of course, would only increase my IP by 900. So, yeah, I guess everything worked out the way it was supposed to. :P