Yeeeah, thank you for your lab!I don't know where the leading /mnt comes from (my guess is the main pool is mounted at /mnt), and I really don't care what happens down the road, but if you change your mountpoint (remove the /mnt from your command), it looks like it will work.
As you can see you tried to
Code:
zfs set mountpoint=/mnt/TestSource/A/moved TestDestination/movethis
but you get
Code:
TestDestination/movethis 96K 2.56G 96K /mnt/mnt/TestSource/A/moved
so you get not that you wanted, real mountpoint is wrong!