differences in traffic logs!

I got a problem with the generated reports. In my company it's a special situation, because there is a other Location who shares the Internet with us. But because of security problems its not allowed to install Netflow on their router! So i installed it on our and watch the outgoing http traffic. In this way i can watch the incoming traffic from their location and check who is the reason ot the traffic.

But now my problem: I just look at the out traffic of all Applications and i see that http is the biggest with 600MB but when i wanna see details and press on http i got only a traffic of 200MB shown. Does anyone know from where i could get these differences??? I think if it is only a few MBs, then it's okay but 400MB is a big fish. Someone is blocking the connection and I can't figure out who it is!!!

thanks for your help