When runnining "duply X status" while running "duply X backup" (sorry, I don't know which duplicity commands are created by duply) due to a race-condition the code of 'sync_archive' might happend to append newly created meta-data files to 'local_spurious' and subsequently delete them. This delete seems to have been the reason that triggered bug 1216921.
The race condition is that the backup command constantly creates meta-data files while the status command queries the list of local and remote files independently over a larger time span. This means that a local file might already been remote but the status command did not see it a few seconds ago.
When runnining "duply X status" while running "duply X backup" (sorry, I don't know which duplicity commands are created by duply) due to a race-condition the code of 'sync_archive' might happend to append newly created meta-data files to 'local_spurious' and subsequently delete them. This delete seems to have been the reason that triggered bug 1216921.
The race condition is that the backup command constantly creates meta-data files while the status command queries the list of local and remote files independently over a larger time span. This means that a local file might already been remote but the status command did not see it a few seconds ago.