Check carefully what unit prefixes your Tixati uses to display bytes in. By default Tixati uses decimal prefixes, and I'm 99% sure the private site displays bytes with binary prefixes. This may be the reason why this discrepancy occurs, or to be more specific, there is no discrepancy, just Tixati and the site use different "units".
Go to: Settings > User Interface > Output Formatting, set Largest Unit for Bytes to: Gi . Additionally, to avoid confusion, disable "Omit 'i' from Ki/Mi/Gi/Ti unit labels". Then check uploaded value for the torrent.
For example:
35.8GB UL in Tixati may be displayed in decimal G (1000^3), while
33.4GB UL on the private site is surely in binary G(i) (1024^3), so:
35.8 * 1000^3 = 35 800 000 000 bytes,
33.4 * 1024^3 = 35 862 976 922 bytes,
it's very close or even the same due to rounding.
uTorrent displays bytes with binary prefixes.
For details see this article:
http://en.wikipedia.org/wiki/Binary_prefixes