When an address has a lot of traffic in one week and
virtually none the next, the previous week's traffic
shows up in the weekly report along with the current
week's traffic from other addresses.
I have attached an IE .mht file (my apologies, but it
was the quickest way to get an example) showing a
report with this problem: see timeframe for graph of
address 10.10.10.193 compared to total graph.
Example report with problem