I had the same problem. See topic:
https://www.ubbcentral.com/forums/u..._5_6p2_Gallery_permissions_we#Post249474Seems to me that something in p2 is changing the permission on its own. I don't think it is a coincidence that this happens also to other people.
Just a thought, couldn't this be a hacking attempt, by uploading malicious images to the galleries?