@isiin
I repeated my test exactly as you showed with a VM, although I reversed steps 7 & 8. (It is only logical (and mandatory) that / be mounted before /home)
The installation completed as expected.
I then tried again but this time I mounted /home before I mounted / (in the order you noted with steps 7 & 8)
This time it gave me the error already noted.
I strongly suspect this is because mounting / after having already mounted /home meant that /home could not be unmounted because it was hidden under /.
Logic and the file system require that / be mounted first since everything else is mounted to existing mount points in the / file system.
Mounting anything else to the same mount point always hides what was first mounted there from the OS. If the installer knows that /home was mounted but it is inaccessible then when it tries to unmount it (before unmounting /) the installer then fails before it unmounts / and that failure will cause anything after that to fail.
This error does not seem like an installer error, but rather a user error in the sequence events were performed.