doors randomly disappearing?

[wfs0801]

So, I'm in the process of building a factory, and I have 2 entrances. Both are double doors on opposite sides of the building. I was working on the basement of the building just a few minutes ago and when I came back up to the ground level both of the doors one side were gone, and one on the other side was gone. What has happened? I tried logging out/in but it did nothing, the doors just disappeared. When I went outside the building I noticed that some grass blocks were missing out of the grassy area that I built in front of the building. I can assure you they weren't missing before, and at first I thought it may have been an endermen, but I've heard endermen can't pick up and move blocks that the player has placed, and I placed these grass blocks and doors (obvious). Is this true about the endermen? or is there another explanation? I've never had any blocks comepletely disappear like this, and I've got quite a substantial (but messy) setup near my original spawn so it's only the first time this has happened.

[warpspeed10]

What difficulty are you playing on?

[nedned2k]

Also, is it possible that someone ninja'd inside your base and stole the doors? Just a thought.

[Zenalia]

I'm going to guess you're playing on hard mode. Zombies can break doors on hard mode. You can either replace them with iron doors or change the difficulty to normal (although since you placed this in the SMP section, unless it's your server you can't change the difficulty). I'm not sure where you heard that about endermen, but unless you have a plugin restricting them from block damage they can pick up dirt and sand.