Can't create encrypted partitions during Debian installation

I am using Debian 7.4 CD. When I set a partition as / during manual partition. It is fine. However when I then try to use it as *physical volume for encryption*... everything works fine it erases and writes random data BUT THEN the mount point / disappears! And when I try to proceed with installation, it says > NO root file system is defined. Please correct this from partitioning menu And when I try to make /, I cant modify the partition to be used as /' because it says No modification can be made. In use as physical volume for encrypted volume I am following [these instructions](http://www.debianuserforums.org/viewtopic.php?f=9&t=460)