you're right, it is transmission. i had the same problem, all of my files would be set as read only. if i tried to delete the offending torrent download files via file manager everything would be set as read only and i had to power off my phone and remove the batt to get everything back in order. the way i found to remove the files was to connect my n900 to my pc and delete them while the phone is in mass storage mode via windows. never had this problem before the last update. im holding off using transmission until its next update, then ill give it another go