Well, I checked and got the following results...
...using acl alone seems to be enough, user_xattr seems not to be needed (to cure this problem).
And it does not seem to be dependent on what desktop you're running, because
without acl in:
Konqueror fails on both KDE and Gnome desktop
Nautilus works on both KDE and Gnome desktop (an on my FAT32 partition).
Well, adding acl in seems to help for ext3, so be it...too bad, there's nothing equivalent for FAT32...maybe some knowledgeable people could investigate, why Konqueror needs acl to work...