Leveling up an ability icon appears on the inventory/item slot area

So in a recent game I had, I noticed that when the icon for leveling up your champions abilities came up, they also appeared upon the inventory area. The icons would be stacked upon one another. They weren't as vibrant as the actual icons above the abilities so it took me a while to notice. I think it's just a visual bug, it didn't really affect my inventory when I clicked on items. I think they also faded but came back when my champion leveled up. (I'm not entirely sure since I didn't play close attention to it during the game). Also, it didn't affect me when I clicked and dragged items in their slots, even if those icons were right on top of the slots. I've only noticed this in one game so far though.