[bug] VSS mount persists if backup is interrupted

Please describe what you are doing to trigger the bug:
Add -vss to backup arguments
Start the backup
Stop the backiup

Please describe what you expect to happen (but doesn’t):
I expect duplicacy to clean after itself – unmount /tmp/snp_XXXXXXX and delete the local snapshot it created with time machine

Please describe what actually happens (the wrong behaviour):

Duplicacy is terminated but snapshot is not being cleaned up.

me@host % tail -f /backup-20200403-214155.log
2020-04-03 21:41:55.898 INFO STORAGE_SET Storage set to sftp://me@[redacted]///Backups/duplicacy
2020-04-03 21:42:03.604 INFO BACKUP_START Last backup at revision 1677 found
2020-04-03 21:42:04.818 INFO VSS_DONE Shadow copy created and mounted at /tmp/snp_072748066
Duplicacy was aborted

me@host % stat /tmp/snp_072748066
822083670 2 drwxr-xr-x 25 root admin 0 800 "Apr  3 16:16:44 2020" "Apr  3 16:11:03 2020" "Apr  3 16:11:03 2020" "Nov 16 13:12:54 2019" 4096 0 0x100000 /tmp/snp_072748066

me@host % tmutil listlocalsnapshots /
Snapshots for volume group containing disk /:
com.apple.TimeMachine.2020-04-03-214204.local <----- this one

me@host % tmutil deletelocalsnapshots 2020-04-03-214204
Deleted local snapshot '2020-04-03-214204'

Based on this article, it sounds like macOS should automatically clean up orphaned TimeMachine snapshots after 24 hours or as space is needed.

It seems like this is a bug; but if they’re automatically cleaned up then the impact seems low.