[CentOS] rsync backup to fileserver - mystery

I have an Intel SS4000E fileserver that I've been using for several years to backup my home directory to.

I have a daily cron job that runs the following command:

rsync -av --delete /home/frankcox/ /mnt/fileserver/backup

I have a directory named misc/sheet-music/classical.  About a week ago I created a new subdirectory there,  /home/frankcox/misc/sheet-music-classical/Russian\ and\ Eastern\ European/

Notice the spaces in the subdirectory name; I don't know if that's relevant or not.

I store a number of bzip-ed pdf files in that subdirectory, like this: BARTOKA.pdf.bz2, BARTOKB.pdf.bz2 and so on.

Now for the mystery.

The rsync command above gets me a report in my email from cron telling me what files were changed or deleted since the last backup run.  And ever since I created that misc/sheet-music-classical/Russian\ and\ Eastern\ European subdirectory, it appears that the files in that subdirectory are getting copied to the fileserver again every day, since they are all listed in the email report that I receive.

diff -r --brief /home/frankcox/misc/sheet-music-classical/Russian\ and\ Eastern\ European/ /mnt/fileserver/backup/misc/misc/sheet-music-classical/Russian\ and\ Eastern\ European/

That command gives me no output, so the contents of that subdirectory appear to match on both machines.

So why is that subdirectory getting copied again every day when it hasn't changed?

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