I do not need a solution (just sharing information)
Over the past few weeks I had seen backup performance on a Windows 2012 R2 box with BackupExec 14.1 Rev 1786 go in the toilet.
Backup rates were on the order of 200MB/min to an LTO-4 tape drive.
Come to discover that patch KB3045313 was the culprit. I uninstalled the patch and the backup rates jumped up to over 1100MB/min.