It seems that this problem happened when moving an attribute from translatable to non transtable, while having content already entered in the CMS. For a freshly created page with those attributes set to 'not translatable', I do not have this problem... I presume that the DB content is not totally correct, and eZp does not know that it has to copy the content from the "main" language, to the others...
If I'm right, Is there any script out there which could handle that? I presume that I'm not the first & only one who ran into that? :)