The list of filenames that is grabbed at the beginning of a "subdirectory scan" ('mb scan -d DIR') is too broad. It uses a string prefix
match that isn't terminated with a trailing slash. Thus, a scan in "factory" grabs also files in "factory-snapshot". This leads to
deletion of all the files outside of the directory at the end of the scan.
(The deletion is supposed to happen only for the files that have disappeared in the given subdirectory; this is implemented by copying
the list of known files into a temporary database table at the beginning, and each file that is seen on the mirror during scanning is
removed from that table. All remaining files are deleted in the end. Thus, if too many files are grabbed in the beginning, they'll be