This may be a bug in BSD.
The RRD graphs had a similar problem where the WAN graph would show "real" traffic metrics, but the LAN graph would show 2x WAN. I think the root cause of that was a bug in the version of BSD that pfSense uses.
The two may be related, but I am not entirely sure. The RRD graphs in 2.2 report properly.
Ok, maybe I can clarify this some. I'm running 2.2.2 (now) and still have the problem. Yes, the RRD graphs in pfSense are correct. However, like many people, I use SNMP to monitor all of my routers (in this case, via MRTG).
SNMP numbers are incorrect on the router at my main site, and now at one remote site. I am using OpenVPN. I can't just reverse LAN numbers, because I'm multi-WAN at most sites - I want to see separate bandwidth for each WAN connection. When I say incorrect, in this case, it means that my outbound traffic numbers are doubled. Inbound traffic is correct.
So, the second site started showing this symptom after I started messing about with the traffic shaping that was on at the remote site. Now, even with traffic shaping off, I am seeing the doubled numbers. I can't fathom why messing about with traffic shaping would cause this to start…but it appears that it did.
Just an FYI - I can report that upgrading from 2.2.2 to 2.2.4 has resolved this for me on all of my pfSense routers.
SNMP is now reporting correct values.