I have a thought here on this...
I believe the guest VMs that have exhibited this problem in the past were ones that had been created early on prior to vCenter Server Appliance being installed in the environment. It was basically created via vSphere before vCenter existed yet... back when just single Virtual Host.
The guest VM had been copied to SAN for testing at some point (via datastore copy) since vCenter wasn't in environment yet and had been running fine for a short while. vCenter Server appliance was then introduced into the environment.
We then use the cold migration of vCenter to move from SAN back to the hosts local storage.
Well... I think above was the progression.
Now... does vCenter have a different range of MAC addresses that vSphere by itself? And then in turn force a change of the MAC address?
The ones with ethernet0.addresstype = "vpx" have beginning MAC of 00-50-56.
The ones with ethernet0.addresstype= "generated" have beginning MAC of 00:0C:29.
I believe vpx means it was assigned from vCenter.
This makes me think any VM that was created prior to vCenter being in the environment will get MAC changed if vCenter migrates it.
Just brainstorming as I need to cold migrate one more and need to know if it will screw up or not.