Chunk Reverts to an earlier state

I had constructed a shoddy wooden staircase to get up a cliff, which I eventually replaced with a much better cobblestone staircase. However, when I save and exit the world, then re-enter, the original shoddy staircase is there again. I've removed the wooden pieces, and they're in my inventory. When they reload and I break them again, I don't get them as items again. I've left the chunk and returned, changed the render distance, and nothing works. Constructions that I've made in other areas after the staircase function just fine.