Trying to post this message again, so formatting might be odd, due to copy/paste.
Scott.
I have a couple of Qs for the original poster on this meter creeping situation:
1: Is your service a 120 VAC 2 wire system??
2: Did the utility company isolate both load side connections??
3: Have they tried leaving the meter in circuit, then jumping across it??
4: What's the power quality over time look like??
5: Is there a possibility that the meter is connected backwards on one side?? or possibly the 5th lug position that's being mentioned here is not being removed??
6: Do you have any high power radio transmitters in the near area, or High Voltage Transmission circuits near your service??
7: Are you absolutely positive that they have used different meters with correct calibrations??
8: Also, are you 100% positive that there's nothing illegally connected to the load side of the meter, but ahead of the main breaker??
Be sure that if the utility company is using insulating boots for tests, that the boots are new, without scrapes or gaps, plus the meter is fitting into the clips, not slipping on the side of the clips.
There's a few tests that could be made to see what's going on when the boots are on. Test voltage drop across the meter with a DVM, run jumpers directly to the load side of the meter, then measure voltage drop and amperes on all conductors, run an electromagnet source near the meter and see if this causes it to creep, stuff like that.
Sounds like a simple leaking meter, or leaky circuitry.
How much did the meter move with the main breaker open?? Are all the poles opening?? Check this with a nominal load [+10 amps per line] flowing, then open the breaker and check voltage drop across it with a DVM. Also check voltage drop with breaker closed.
When checking voltage drop, use a DVM with low to medium input Impedance [nominal loading effect]. Check from the "Line" side on one pole, to the "Load" side of the same pole - not to ground!!
Start at the highest V setting, then work down to the lowest possible.
With a current of 10 amps flowing across a 100 amp breaker, expect a voltage drop of 3 volts max. [the DVM will measure 3 VAC].
Check amperes with a True RMS [high Hz] type meter. For low I levels, use a flow-through ammeter with high accuracy and low loading effect.
Scott SET