Why does "Umount /home" doesn't work after "ecryptfs-mount-private" ?

Issue

• "Umount /home" doesn't work after "ecryptfs-mount-private"

Neither root nor init during shutdown can execute "umount /home" successfully, when the encrypted
folder '.Private' gets decoded in a session with"ecryptfs-mount-private". Afterwards, the error 
appears independently from '.Private' being separated or no.

Error message:

umount: /home: device is busy.
        (In some cases useful info about processes that use
         the device is found by lsof(8) or fuser(1))