Files missing from backup

I am evaluating Backup Exec 2014 and I have encountered some serious issues with my backups – files are missing from the backup.  My initial backup of a full machine was missing over 20gb of data. In tracking down a reproducible case, I have narrowed it down to the following (again, this is just an example):

• Create a Backup to Disk
• Edit the selection to include several files in the c:\inetpub\custerr directory (namely 500.htm, 500-100.asp, and 500-13.htm)
• After the backup completes, try to restore files from that backup. Note that “500-100.asp” is not present in the backup

If I turn on full logging, I see that 500-100.asp is also not included. It doesn’t matter what I include in the backup select, 500-100.asp is never included (this is true whether the backup is local or of a remote machine).

Again, this is just an example of almost 20gb worth of data that wasn’t backed up.  

I am running this on a Windows Server 2012 R2 Essentials with all patches applied, and all patches are applied to Backup Exec 2014. There is nothing in the “global exclude selections”

I'm sort of at a loss as to what to do next... this is a pretty vanilla installation so I don't know what could be special. On the other hand, its a pretty devastating bug to have not been found yet (a backup program that fails to backup).

Any thoughts?