efficiency is a bit nerfed in minecraft 1.4.6. e.g. Efficiency V Pickaxes no longer instantly break dirt. but with the forge 126.96.36.1991, the pickaxes still instantly break dirt. In the multiplayer mode, it seemed that a dirt block is broken instantly and disappear from a player. But the block was not breaking. There is nothing the player can do for the block except to relogin.