In RouterOS 7.20.1, the MTU is incorrectly assigned to a VRRP interface if the parent VLAN interface is created on a bonding interface. The MTU for the VRRP interface is taken from the bonding interface, not the VLAN interface.
What's new in 7.20 (2025-Sep-29 12:33):
*) vrrp - make MTU property read-only;
