Digging a old topic I found while looking for a fix for the same issue on different hardware/os.
I have a couple answers to add that could help better understand this issue.
How/Why? MAC addresses are NOT supposed to change, EVER.
(...)
Very annoying. I'm not sure if it is hardware or software, but personally I am leaning towards software given the kernel code that I've seen posted.
The MAC address is the equipment is not changing, the one the OS gives to the equipment is.
It is supposed to do so to deal with faulty hardware and driver which returns an invalid MAC address, using the invalid MAC would further break many things so as a workaround when and invalid MAC address is detected, the OS uses a random one instead.
This is usually triggered by a software issue with drivers returning the wrong MAC address, a common case is the MAC being reversed.
RFC 2469 addressing this issue has been aroudn since late 1998 but the issue still lives today, see tools.ietf.org/html/rfc2469
The odd thing about it is that it seems to affect just a certain range of addresses and not all addresses used for the GNex.
It has to do with reserved type addresses and misreading the canonical form of a MAC address or LSB format.
As explained in the RFC linked above:
LSB format is best defined as how the bit order of an adapter address on the LAN media maps to the bit order of an adapter address in memory: The first bit of each byte that appears on the LAN maps to the least significant (i.e., right-most) bit of each byte in memory. This puts the group address indicator (i.e., the bit that defines whether an address is unicast or multicast) in the least significant bit of the first byte.
When the MAC address is read with inverted byte order, it means every last digit higher than 7h will trigger the multicast type case during attendibility check and cause the MAC to be deemed invalid.
It could be something different triggering the issue, but chances are some range are unaffected because when read wrong they're still part of valid range and not falling into a reserved one.