Comment 13 for bug 2031482

We do not use hardware sync and it is not enabled.
The logic applies like this:
dhcp serves pxe boot or dhcp requests to a machine
whatever vlan id was configured on the switch port for that machine determines from which vlan will dhcp server receive request and which ip address it will assigne (no ip overlap limitation).
DHCP server politely informs maas what was done - which ip and vlan were assigned / observed.
In the interfaces.py the logic to 'fix' stuff makes global adjustments to vlans and subnets. In our case, a subnet was shifted to a different vlan but id probably depends on topology.

I am 99% sure if not node_is_commissioning() is incorrect for determining if server is a rack or region controller and it is triggering this global shuffle of subnets.