I have been able to make some additional observations. Son loaned his 645 to me to use for comparison, and I found his Contax and mine behaved in exactly the same manner. This would suggest that the bodies are functioning properly.
When using the Metz flash (with SCA 3802 adapter) in TTL mode, camera set on Av, I got inconsistent results from both bodies. Some pics were 1 stop underexposed, some were 2 stops overexposed, and on occasion I would get one properly exposed.
However, I also tested with a Contax TLA 200 flash. Same settings all around. Now, both bodies shot 2 stops overexposed, consistent with the info from Phase regarding flash overexposure on this body. And when I set the EC to -2, I was able to get properly exposed pics with great consistency.
I don't know why the Contax flash behaved properly but the Metz did not. I would suggest that it is due to some problem with the Metz adapter, but I do not know if it is a malfunction or if the adapter just wasn't designed/programmed properly.
Oh, yes, one more thing. Under natural light, I found both bodies had a tendency to underexpose about 1 stop.