Well, whenever I place a block, it does not show up for a loooong period of time. Whenever I break one, it becomes a ghost block for another loooong period of time. Also, block updates such as turning on a redstone lamp or flicking a lever visually never happen for a while.

So far noticed with: redstone lamps, levers, nether brick fences, grass blocks, wood logs/planks, buttons and doors (wood and iron).

Thanks!