On the snapshot 14w07a punching a tree in sunlight below the leaves will break like normal then start flashing between light and dark. I've only found oak trees so I can't say its the same for all. I've just checked this on birch trees, and found something very interesting. While I was punching the birch tree there was no cracking of the tree at all. I punched it for a while then it broke.
I have also noticed this. But for me the blocks teleport to empty space behind me. I'm very wary when it comes to mining diamonds now. It doesn't seem to matter what block it is that Is mineable and doesn't happen every time. I only noticed it when I was mining near lava and would hear the sound of the items going into the lava but the lava was 10-15 blocks away.