There was multiple updates on 1.7.4, but i've noticed that on all of them, when you destroy a block, about 10 Game Ticks after, it reappears. For example: you are in a jungle, blocked by trees. You destroy the Leaves, and clear a path, but all of a sudden, you teleport right back to where you were when you had mined those leaves. So far, Entitys aren't affected.