Steps to reproduce:

1. Monitor a linux computer running ZFS
2. Add Template OS Linux
3. Create a ZFS volume
4. Add enough data to the volume such that it hits the 20%
5. Get problem:

   Free disk space is less than 20% on volume /zpool/volume/to-be-deleted

1. Delete the volume zfs destroy zpool/volume/to-be-deleted
2. Wait

Result:

• Latest data stops showing Free disk space on /zpool/volume/to-be-deleted, Total disk space on /zpool/volume/to-be-deleted, and Used disk space on /zpool/volume/to-be-deleted.
• The problem doesn't go away 

Expected:
As the volume no longer exists, the problem should be resolved.