During a backup some Windows system files are not being backed up by the Backup Client, for instance
This happens because Windows specifies files that must not be backed up in the following registry key:
For details see http://msdn.microsoft.com/en-us/library/bb891959%28VS.85%29.aspx
The backup client filters out these files from any backups done by VSS. According to Microsoft these files should not be backed up and is not required for restore.
A typical example of the registry entry looks like this:
This is intended behaviour and does not require a fix.