It is a common misconfiguration. Given a line
  device  dir  type  options  garbage
in /etc/fstab, some umount versions will complain "device busy"
when the umount fails. Thus, it is better to use
  proc    /proc     proc
  devpts  /dev/pts  devpts
instead of
  none    /proc     proc
  none    /dev/pts  devpts
so as to avoid this silly "none busy".
But many distributions come misconfigured like this.
These days umount is done by directory, not by device,
since a device may be mounted multiple times, so
I expect the silly message is gone.
(Is your umount recent?)
[But this is only about the "none". I don't know what is
wrong in your situation.]
Andries
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