Comment 3 for bug 1843328

Thank you very much for your answer. This is what I tried after it:

1) After running "sudo fsck.vfat -r /dev/sdb1" and connecting under Windows, the problem is not present.
2) On linux, running "sync" in a loop, the problem is not present (and fsck does not report any problem.
3) Without the "sync" loop, the unmounting happens again and the dirty bit is set too.
4) Also, if I just mount the device and access through the file manager (Calibre not running), the problem does not happen either.

In my little understanding, it looks suspiciously similar to bug 1834641.
Do you have any advice?
Thank you in advance