That is the “old way” of configuring VLANs and can cause potential issues, see https://wiki.mikrotik.com/wiki/Manual:Layer2_misconfiguration
There is a good tutorial on the “new way” http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1 and descriptions in the Wiki https://wiki.mikrotik.com/wiki/Manual:Interface/Bridge#Bridge_VLAN_Filtering