[Gameplay] Shop is bugged, won't let me buy items

I was playing Thresh and this bug occured (see picture in the link). Think it has happened to me once before, and it is really annoying. As you can see in the link, the shop indicates that I can buy items that I cannot afford, but when I try to buy them, it doesn't work, so it has to be a visual bug. Earlier in the game, I had the Aegis and null-magic mantle and about 1k gold. When I tried to buy the locket, it didn't work, so I had to sell the components and then buy the locket.

I have no clue how to recreate the bug, and it has happened to me on two occations I think.

Would appreciate some feedback :)