Well, if there were no logs to backup, then they will be empty.. There was a bug (a very long time ago) for the monthly rotated backup logs.. but that was fixed.. make sure you have the latest version of DA.
I just experimented backing up an account so I can delete an account, create a reseller account with same username and then restore backup, alot of files were missing from backup. It's late now and I will add further info in morning......
Hmm.. I'd have to have a look at the system. If you want to send me the root details to [email protected], I'll be happy to see what's up. Also include a sample domain that this is happening for (active domain).