I was playing on a server in the new pre-release and looking in the ice plains for a new structure (being the igloo) and I came across this one. Knowing about the structure already I knew that there was a hidden basement below the carpet with villagers and stuff. I broke the whole floor and all of the carpet and found nothing. Now I didn't do much research so I wasn't sure if there was only a chance of there being a basement but I wanted to report it anyways just in case. Like I said, I'm on a server so I can't get the seed so don't bother asking.
EDIT: If you're wondering, no one touched the igloo before, these are all new chunks.