[CentOS] Centos 7 and MAC address munging

Odd situation: I've mentioned before that I have several users for whom I
have to spoof the MAC address, due to a software license. Now, I've got
net.ifnames=0 biosdevname=0 on the grub2 command line, and I've got the
spoofed MAC address in /etc/sysconfig/network-sctipts/ifcfg-eth0.

But he had a serious problem - X froze, and he thought to reboot, rather
than call me. It came up with the actual MAC. I tried a number of things,
including reboots, but the only thing that worked was systemctl stop
NetworkManager, ifdown eth0, then ifup eth0, then start NetworkMangler,
and all was good.

Yeah, I know, afterwards, I remembered I should have use nmcli....

But the real question is *why* did it fail on the reboot. I find no clues
in dmesg, or messages, or boot.log.

Clues for the poor?

       mark