I'm doing backup from win98 workstation using smbtar.
With smbclient 2.2.8a all is OK, here is resulting file:

rw-r--r--    1 root     root     348904448 Feb 11 10:56 backup.tar

And smbtar output:

tar: dumped 1404 files and directories
Total bytes written: 348270592

I used following command:
 /usr/bin/smbtar -s korotkova -p password -x SBRF -t /BACKUP/sbrf/backup.tar -v

If I do the same with smbclient 3.0.2 backup.tar grows to more that 3Gb and
smbtar continue to work...