I went to my melon farm to see that there had been some minor grief. Now, it's not enough for me to be upset about or call an op, as no permanent damage was done that couldn't be fixed in several seconds flat. But what was interesting was the fact that it happened within range of my diamond protection stone. I did a /ps who just to check whether it was active, and it says "no fields found." I haven't been on a whole lot recently, so I have no idea when it could have happened, but I have two diamond protection stones that have simply vanished, as well as a coal (but I just repurchased that one easily and placed it, which reenabled it, so I won't bother with that one).
The weirdest part: exactly where I put my diamond, there was a block of blue wool rather than the stone.
They did work the last time I was on (and yes, "/ps on" says it is already enabled). Anyone have any clues as to how this could have happened?