Comment 1 for bug 818432

After these users are logged out, and when you're listing their $HOME directories, can you please confirm that their home directories are NOT mounted, according to /etc/mtab and /proc/mounts?

You will see data there if these directories are still mounted, but when they're not mounted, you should only see a very basic skeleton like this:

$ sudo ls -alF /home/foobar/
total 8
dr-x------ 2 foobar foobar 4096 2011-12-27 11:01 ./
drwxr-xr-x 7 root root 4096 2011-12-27 11:01 ../
lrwxrwxrwx 1 foobar foobar 56 2011-12-27 11:01 Access-Your-Private-Data.desktop -> /usr/share/ecryptfs-utils/ecryptfs-mount-private.desktop*
lrwxrwxrwx 1 foobar foobar 32 2011-12-27 11:01 .ecryptfs -> /home/.ecryptfs/foobar/.ecryptfs/
lrwxrwxrwx 1 foobar foobar 31 2011-12-27 11:01 .Private -> /home/.ecryptfs/foobar/.Private/
lrwxrwxrwx 1 foobar foobar 52 2011-12-27 11:01 README.txt -> /usr/share/ecryptfs-utils/ecryptfs-mount-private.txt

Also, can you confirm the permissions on the user's home directories when not mounted? As you should see above, the unmounted user home directory should have permissions 500 dr-x------. Note that not even the owner has write permission here. This is to prevent exactly the situation you're describing -- inadvertently writing cleartext data to the home directory.