IP Groups and device stats do not add up (5.5EA)

Hi,

I am currently running version 5.5 EA and have the following problem.

I have setup a number of IP Groups mostly containing single IP address which are then being used in the scheduled reports so we can do billing. I have been comparing the figures with our current billing system and all seems fine, but then I noticed that if I enter the interface which all this traffic is for and goto the destinations tab for the same time period as the IP group they show different figures. The one on the interface can be as much as half the amount as the ip group. I only have 2 interfaces being managed and I did check the 2nd interface just to make sure it did not have any traffic report against it for the IP address and it didn't.

So I am wondering why the big difference?

Thank you
Tim