What version of CWM are you using? Some of the older varieties had issues with restores - the one found here has worked fine for me when restoring nandroids.
Backup/restore is only working in the latest orange CWM dated 8/17. Beware if you're on Gingerbread though...some combinations of CWM, kernel, and ext4 causes /data wipes on Gingerbread and makes and backups/restores useless.
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