While I were trying to expand and improve my base in the End, at a certain point blocks I placed just jumped back into my inventory. I still can mine blocks, but placement is impossible without WE. This glitch only occurs in a certain chunk or two.
I don’t know the exact position of this chunk, but if you are on the surface, you can see a rectangular gap near Zingwoof’s town. The problems start around that part.
They were fixed in the past. We ran a program that programatically checked every mcregion chunk file for the errors and fixed them.
I think this is more a Bukkit/Minecraft issue. Chunk errors otherwise would be spamming the console with 50 messages a second and crashing the entire server everytime someone went to the chunk.