samba - Dec 2004 - XP NTBackup Inconsistency - du under-reports vs file size

(Sys config info at bottom)

Use XP ntbackup.exe output to Samba share for several years and never had a 
problem.  Backup size would range between 10 and 15 GB.  Would always 
perform a verify after the backup.  A few months ago the process started 
failing at the verify stage.  The backup appeared to complete successfully, 
but as soon as the verify process started a message "Error: An 
inconsistency was encountered in the requested backup file." would be
received.

Checked the backup file and noticed something strange.  The file size 
listed would be as expected 10+ GB, but the du command output stated 
4KB.  The process has been repeated numerous times (very difficult with a 
2+ hour cycle time).  I have even performed a du on the file while it is 
being backed up and  it grows fine, until a some arbitrary point it drops 
way down, goes up and down a bit, but is always grossly under what it 
should be.

I apologize for not even knowing how to get the appropriate version/release 
information.  Below is what I do know:

Client OS: XP SP2 (note: I think I have not had a clean backup since 
applying SP2, thus this could be a source to the problem)

Server Info:
Redhat Linux
output from "uname -a"
"Linux linux 2.4.7-10 #1 Thu Sep 6 17:27:27 EDT 2001 i686 unknown"

Samba man page version heading states version 2.2 - I have not done any 
reinstall so that is probably correct.

feel free to request additional information (if it involves Linux system 
info, please provide instructions - much thanks).