Thank you for your explanation. I suspected it is bug yes. But I am also not comfortable to go with Kodi 17 Alpha. I made some research and done it in an old fashion and dirty way. So for future reference and if there is really no other way to do it, you can do it this way:
1. tar the whole /storage dir to a /tmp folder. Copy with scp or samba out of the box
2. Copy the archive back to a new box, I used /tmp
3. Stop Kodi: systemctl stop kodi
4. Remove hidden and non hidden files from /storage
5. Restore from the archive to /storage
6. Reboot
That's all.
I suspect the bug is somewhere around step 3. If I copy without stopping kodi.bin then I get the same result as restoring from backup.