On Snow Leopard 10.6.8, TimeMachine keeps backing up the same files over and over again, as if they were not backed up the first time. As a result, each time I get a full backup of 300 GB!
I checked the Backups.backupdb folder tree and looked at "snapshots by date" (e.g. 2012-07-06-201030). What is strange is the files TimeMachine backs up have exactly the same MD5 checksum for each backup.