I'm testing from the latest hardy livecd. And your keyword does not show up.
It looks like your image contains this in the xmp.Subject field.
$ exiftool -xmp:all DSC_0407-2.JPG
Subject : vacances, Saint-Tropez
If I copy the tags from this image to a copy of the same image with
exiftool -tagsfromfile DSC_0407-2.JPG DSC_0407-2-copy.JPG
they are visible in eog under the Keyword tag.
If I just write the same tags like this
exiftool -xmp:Subject="vacances, Saint-Tropez" DSC_0407-2.JPG
They are also visible in eog.
Just a comment to antistress
I'm testing from the latest hardy livecd. And your keyword does not show up.
It looks like your image contains this in the xmp.Subject field.
$ exiftool -xmp:all DSC_0407-2.JPG
Subject : vacances, Saint-Tropez
If I copy the tags from this image to a copy of the same image with
exiftool -tagsfromfile DSC_0407-2.JPG DSC_0407-2-copy.JPG
they are visible in eog under the Keyword tag.
If I just write the same tags like this "vacances, Saint-Tropez" DSC_0407-2.JPG
exiftool -xmp:Subject=
They are also visible in eog.
So maybe this is a F-Spot bug?