Not sure if this helps (and I have not used MRTG) but I did some researching on the net where others had some similar issues and most of the fixes from groups on the net claim that the mrtg.cfg file usually has excess junk left from the example or defaults. They suggest reduce it to just the things needed for monitoring otherwise you get improper results. Our build is SNMP v2 and v3 and version of MIB is MIB II. Wish I had more info on this for you.