Ok guys, in case you don't believe this there is a video on my Youtube channel.
I was on a world in creative, and going to build some Pacman buildings. I saw some sand missing and some stone, but I thought it was some Minecraft thing and flew off (I'm not suggesting this is Herobrine as I don't believe in him). I was looking for a place to start when I saw a skeleton with a pumpkin on his head, so I asked my friend what they thought. They said to cage it in case it was extremely rare (Might be). So once I did that I flew off to kill another skeleton I saw with a pumpkin to see if it would drop, it didn't. I saw a zombie with a Jack O Lantern and caged that to. I flew back to see my skeleton when I saw it had vanished! (It was day, however there were no drops and I did but water underneath it, it was in the water). I flew of to check the zombie that I caged (The one with the Jack O Lantern) and it was there. I flew off to find even more of these mobs, and then when I went back to my zombie it was gone!

What are your ideas?