Shared folder set up in VirtualBox, but contents are not shared

Question

I set up a shared folder between the host system and the VM (Debian). I set it to Auto-mount and enabled "set permanent" via the VirtualBox GUI.

I then enabled the folder (named PRED_share) via VBoxLinuxAdditions.run . As expected, I was able to access a new folder in /media , /media/sf_PRED_share.

However, when I created files in that directory, I did not see them in the host's folder, and files copied to the host's folder were similarly not available in the VM's folder.

In essence the two folders are separate. How should I proceed to actually enable the sharing of the folder?

Notes: For

sudo su
mount

the output was

/dev/sda1 on / type ext4 (rw,errors=remount-ro)
proc on /proc type proc (rw,noexec,nosuid,nodev)
none on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
none on /dev type devtmpfs (rw,mode=0755)
none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
none on /dev/shm type tmpfs (rw,nosuid,nodev)
none on /var/run type tmpfs (rw,nosuid,mode=0755)
none on /var/lock type tmpfs (rw,noexec,nosuid,nodev)
none on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
gvfs-fuse-daemon on /home/ppuser/.gvfs type fuse.gvfs-fuse-daemon
(rw,nosuid,nodev,user=ppuser)
/dev/sr0 on /media/VBox_GAs_5.2.1 type iso9660
(ro,nosuid,nodev,uhelper=udisks,uid=1000,gid=1000,iocharset=utf8,mode=0400,dmode=0500)
binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc
(rw,noexec,nosuid,nodev)