Traffic graph showing negative values

[idmud]

Hi,

I have pfsense virtualized on a esxi5 whitebox. The only minor issue is that the traffic graph will show negative values during high-io load, such as this wan-interface

I'm guessing it's a clock issue with the guest/host causing these timing problems, anyone seen this before and know of a solution? I've tried adding kern.hz=100 to the config file with no difference. Nics are not configured in passthrough mode but connected to virtual switches. This happens from 1.2.3->2.1 that I'm now testing.