This happened to me earlier today, but then It stopped.... I made a pe saying when I broke blocks I got nothing from it, I couldn't open chests or doors... and then it stopped... I was at Yields Spectacular Diggy Hole event, when it happened again! 50 seconds to go, I couldn't open the chest... so I did some experiments -- Here they are! I have more, I just felt like those were the best ones.

http://img819.imageshack.us/img819/8552/20120807194554.png

http://img442.imageshack.us/img442/7492/20120807193621.png

http://img805.imageshack.us/img805/3294/20120807194657.png

http://img846.imageshack.us/img846/9030/20120807194459.png

If that worked ( I can't preview them? )

Im no pro, so you'll just have to click the link I suppose... :c

That is... Interesting... If I had to guess, your client stopped communicating with the server during that period. I don't really have a solution other then trying to disconnect/reconnect to the server next time it happens.

lol, the ultimate grief. you will never get caught because it never really happened!