md5sum -c failing on some files after rsync backup

[Timo Veith]

Hello list readers,

I am doing rsync backups based on Mike Rubels recipe 
(http://www.mikerubel.org/computers/rsync_snapshots/). I am creating lvm 
snapshots of partitions whose contents changes fast. In order to verify 
if evyerthing went ok, I do md5sum checks on all files and everytime some 
files are failing the test. Here is a list of them:

./amavis/db/__db.001: FAILED
./amavis/db/__db.002: FAILED
./amavis/db/__db.003: FAILED
./amavis/quarantine/spam-Tj3tsKAU7G3c.gz: FAILED
./amavis/quarantine/spam-VyKl+vwlBxlY.gz: FAILED
./amavis/quarantine/spam-pAMwYjbMNhuP.gz: FAILED
./amavis/quarantine/spam-36fTxT+IWOPS.gz: FAILED
./amavis/quarantine/virus-tvUARLx2txFB: FAILED
./amavis/quarantine/spam-Zli5v0qZSomA.gz: FAILED

At first I wasn't stopping services on that machine, because I thought 
that taking snapshots with lvm would give me a consistent state of the 
filesystem. Ok, maybe I really have a consistent state and rsync is to be 
blamed. However, I also stopped amavisd-new and all other services before 
I did the lvm snapshot and I still get the above failures.

Any ideas why this happens and how I get rid of the errors?

TIA and kind regards,

Timo