Cannot place blocks at Y=255

After creating a block at Y=255 for no apparent reason using commands, I wanted to see if i could put another block adjacent to it. However, it appears that I could not place a block there. In my world in 1.7.9, I could place blocks at Y=255, but it appears I cannot in the current update. The picture shows me trying to place an polished andesite block next to the light bIue wool, but the andesite does not appear. I hope this is not a duplicate.