Looking  through the current HTML manual I see:

“In addition, if you move a directory rather than copy it, the files in it do not have their modification time (st_mtime) or their attribute change time (st_ctime) changed. As a consequence, those files will probably not be backed up by an Incremental or Differential backup which depend solely on these time stamps. If you move a directory, and wish it to be properly backed up, it is generally preferable to copy it, then delete the original.”

and

“As noted above, if you move a directory rather than copy it, the files in it do not have their modification time (st_mtime) or their attribute change time (st_ctime) changed. As a consequence, those files will probably not be backed up by an Incremental or Differential backup which depend solely on these time stamps. If you move a directory, and wish it to be properly backed up, it is generally preferable to copy it, then delete the original. Alternatively, you can move the directory, then use the touch program to update the timestamps.”

Why?  Shouldn’t bacula treat these as a newly created directory with new files in it, and back them up?    This is a big burden requiring people to remember whether they should use cp or mv to move files.  Besides this, and the disk space issue, mv is a simple pointer redirection, and might be faster than a cp depending on how high in the tree you are working on.