Inventory problems!!

I have noticed some times when I am updating my inventory after a MTG purchase that when I go to that particular card in my inventory it shows my total either to MANY or not ENOUGH. I am not sure what is happening but I know I am not doing it myself; I tried an experiment and it happened again; I hope the owners of this site do not make changes to my inventory for NO reason, if so, I guess it is time to look for another site to save my inventory, Thanks.