[SHOP] If i have health potions in my inventory and go back, i can't buy another one???

If I'm playing Ghostbride Morgana on Summoners Rift and I have to go back when i still have health potions in my inventory I can't buy another one. I can click it, but nothing happens. It's really annoying if I have one left and want to lane with more and can't buy any more. :( Unfortunately I don't have video proof but this happens all the time. No Idea what's wrong.