Kodi 18 - 'cannot save setting' for backup location on usb

[jakenl]

RP1 2B
Kodi 18, latest on stable release

I used to run daily/weekly backups on home folder and system. Place of storage was a plugged in additional USB stick. I had some issues since I converted the OS from SD to a dedicated USB-stick.
Afterwards I also formatted the additional USB-stick from NTFS to exFAT, because during my trials with the 'USB-OS', sometimes the NTFS stick was recognized properly, ther other time it wasn't.

The XBIAN config setting in the GUI allows me to select a folder for backup of home and system. As long as I choose a location in my /home folder, it goes well, but when I select a folder on the mounted additional USB stick, the 'do you want to save' setting results in a notification 'cannot save setting' followed by xbian-worker updated'. The backup location is always renamed back to to previously given /home directory.

Since backing up on the additional USB stick always worked, do I wonder what is going on. The kodi.log doesn't say a thing, unfortunately.