Mikrotik have a default native VLAN ID of 1 on bridges (for the switch-to-CPU interface) and bridge ports, as with many other defaults it doesn’t appear in /export. Attempting to add an /interface vlan with the same ID usually results in odd behaviour and/or loss of connectivity due to the mix of tagged and untagged for the same VLAN.
A Mikrotik bridge has two personalities - it is both like a switch, and like an interface to resources provided by the CPU, see http://forum.mikrotik.com/t/routeros-bridge-mysteries-explained/147832/62
If you are familiar with Cisco the following may be useful http://forum.mikrotik.com/t/why-does-this-work-with-cisco-and-not-with-mikrotik/156721/3 http://forum.mikrotik.com/t/vlan-issues/143197/6
Most Mikrotiks only support hardware offload on a single bridge, additional bridges will pass all bridged traffic through the CPU leading to significantly less than wire-speed performance. You will also require additional configuration for L3 hardware offload.
If you are going to configure any access or hybrid ports also be aware there should only be a single VLAN ID specified for bridge vlans vlan-ids= when that ID is used untagged. You should only specify multiple VLAN IDs when all of the IDs are used tagged on trunk ports.
@anav for whatever reason /export in some versions of RouterOS on some hardware quotes the bridge vlan interface list(s) unnecessarily.