XnView Software

As I am working with Gramps and image metadata a fair bit, I have just installed XnViewMP 0.86 under Mint 18.2 and have come across a curious issue, possibly related to UTF-8 & German Umlauts, perhaps not.
I am attaching two screenshot and basically the issue is that, under Linux, in the categories pane, a 'ö' character in a name does not display properly, but a ' ß' does.
While under Windows, viewing the same file, in the same metadata item, the name shows as expected.
I realize that the two copies of XnViewMP do not have the same set of categories, as I have not transferred those, but, assuming the less complete set in the Linux installation all came from the image metadata, I am puzzled why they might differ for the one item I have found at this time

if categories are from IPTC, please check Settings>Metadata>Encoding

It was set to Locale for both Win 10 & Mint.

But ... after doing more low level testing of the actual image files on the two machines, I have to check out some other issues with the software that backed up these files and that which unpacked them.
For now at least, there is a difference in the files and I no longer think it is a problem with XnViewMP