It seems to only happen in multiplayer, It takes about 1-2 minutes of playing for it to occur. I have tried re-loading the game more than once and that has taken no affect on it. I've tried deleting my .minecraft to see if it was a file I had that was causing the problem. It never happend before until now. I haven't tried re-downloading the client, but I doubt that would work.
It's also not just the placed blocks even the blocks I have in my inventory are 'invisible', but my tools aren't. Some blocks you can see like: Chests, and signs.