Anyone got an idea yet?
Not me although it makes me curious. Normally FAT32 doesn't bother with permission stuff as far I know. In fact I used to use a fat partition to get rid of these by copying worrysome files to FAT32 and then access them from any account without a hitch.
So I wonder what is up here.
Did you try to copy the files to your PC with any account, reformat the media to FAT32 and then move them back? Maybe that takes away some spookiness somewhere in the process. My best shot for now. Hope still better ideas will come by (as I am wondering just like you).