Tiger-compatible versions of Retrospect up through 6.0.212 with Driver Update 6.4.102 have run into problems in duplicating and backing up Spotlight-indexed volumes.
EMC/Dantz tech support's workaround is to use two exclusion selectors in scripts or commands for duplicating/cloning and for backing up:
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050802192637718