interface_bridge_add_member is inadequate for adding a bridge member that may have not existed at the time of bridge interface's creation. interface_bridge_configure on the interface's bridge ensures all settings (private, etc.) are applied. Ticket #4312
Related issues
Bug #4312: Bridge advanced settings not always applied after interface is added to bridge
interface_bridge_add_member is inadequate for adding a bridge member that may have not existed at the time of bridge interface's creation. interface_bridge_configure on the interface's bridge ensures all settings (private, etc.) are applied. Ticket #4312