The bug has been introduced here https://code.launchpad.net/~ack/maas/+git/maas/+merge/406360 .
In short, in MAAS < 3.3 we moved the subnets to the new VLAN only when the VLAN of an interface of a CONTROLLER was changed.
From MAAS >= 3.3, whenever the VLAN of an interface is updated we move the subnet to the new VLAN.
The bug has been introduced here https:/ /code.launchpad .net/~ack/ maas/+git/ maas/+merge/ 406360 .
In short, in MAAS < 3.3 we moved the subnets to the new VLAN only when the VLAN of an interface of a CONTROLLER was changed.
From MAAS >= 3.3, whenever the VLAN of an interface is updated we move the subnet to the new VLAN.
In order to fix this, we have first to fix https:/ /bugs.launchpad .net/maas/ +bug/2064281 on 3.5 and backport it to 3.4. Once the backport has landed, we can fix this bug.