MC 1.6 Carpet Bug

I played a game file I had been playing for a while in version 1.5.2. I then opened the same file in version 1.6, and added carpet to a room in my house, then saved and quit the game. I then reopened the game using 1.5.2, and the carpet was gone because version 1.5.2 does not support carpet. However, when I reopened the game file for a third time in 1.6 prerelease, only a portion of the carpet had returned.