Mejais stack bug

I just experienced a bug where I bought mejais and had 8 stacks. I sold the item due to being behind and then I bought a dark seal. After that I then upgraded it to a mejais since we were winning again. I noticed that I not only had my 8 original stacks, but I had the 10 additional ones on my regular dark seal, for a total of 18. What gets insane is that I sold my mejais again and bought another dark seal and bought mejais again; giving me 25 stacks. Hopefully I don't get banned but, that's riots game-breaking bug.