LS Network Monitor Traffic Map Inactive

LS 3.1.1 on Mac OS 10.8.4 (with Server running) there is all kinds of network activity, as one would expect. However, the LS network monitor graph shows nothing, even go so far as to incorrectly state the time of last activity (by a massive longshot!).

Here's what it looks like:

https://www.dropbox.com/s/9qt4w7vmn4xliqy/LS-Network-Monitor.png

Any ideas what could cause the network monitor to think there's no activity? If you look carefully at the screen grab you'll see there's activity going on at that very moment...

Thanks