Data Domain: Empty Retention-Lock DDBoost Storage Unit does not delete

For example, see the following situation:

# ddboost storage-unit show My-Storage-Unit
Name            Pre-Comp (GiB)   Status   User          Report Physical   Tenant-Unit
                                                           Size (MiB)
-------------   --------------   ------   -----------   ---------------   -----------
My-Storage-Unit            0.0   RW       ddboost                     -   -
-------------   --------------   ------   -----------   ---------------   ----------- 

# ddboost storage-unit delete My-Storage-Unit

The 'ddboost storage-unit delete' command will delete all files in the storage-unit.
        Are you sure? (yes|no) [no]: y

ok, proceeding.

**** MTree "My-Storage-Unit" has retention-lock configuration, can be deleted only if it is empty.

Despite the storage unit reporting 0.0 GB, it does contain files or directories. The combined size of the content is smaller than one tenth of a GB.

To check, search any autosupport report for the directory manager statistics "DM STATS" and review the entry for the offending MTree:

DM STATS for Active context -- uptime=8611998s, mtree_count=76, inode_count=398777, snapshot_count=93, DM_size=779878400

0: Utree,1594993679,#Inode=256,nInode=46,#dir=254,dm_utree:d0000,1,0,400,6,0,c71b1805,cd476dfd,185c4523,5db3f,6001121,7b2e1268:,size=851968,version=0x2:0x0
1: backup,1594993680,#Inode=5,nInode=18,#dir=3,#snap=0,nSid=112,dm_mtree:40000010000,1,0,400,6,0,fafc75d5,c882feab,4f8936af,16d0624e,2698adb0,1a558321:,size=393216,RW
2: My-Storage-Unit,1600882434,#Inode=10,nInode=366961,#dir=3,#snap=0,nSid=20834,dm_mtree:40000010000,1,0,400,6,0,99e73efb,e2bd7763,aefc5bde,ad128a79,477cfeb9,d1e8a7fa:,size=10944512,RW

For the storage unit, #Inode is reported to be 10, whereas for an empty MTree it should be 4 instead. Hence there are still some files that must be deleted from the storage unit first.