Yeah sometimes the store portion bugs out, so it doesn't take into account the increases/decreases, but it'll regulate out eventually.
I had it the other day where I purchased a skin and it didn't take my RP for a full day.
lol i am sure u were super happy and when they took your RP .. you were like FK S***CH ! :D
At first I was excited, then when I tried to make a purchase and realized it numerically counted the RP gone even though it didn't show it was missing.