crippled capital letters

Hi!
Thanks to the good instructions, I made an OMV 5.0 installation on a Raspberry Pi 3b + straight away. Everything works perfectly from Windows 10.
When I backed up my Next Cloud Server to the NAS, I found that all capital letters in the file names are replaced with ";" and a number.
The backup itself works perfectly.
I do the backup with:
"rdiff-backup --force / var / www / nextcloud / data / mnt / nas /"
where "/ mnt / nas /" is mounted to the directory on the NAS.
File system is ext4 on my Nextcloud and on my OMV storage.
Is there any setting I have got wrong?
Any help appreciated!