This is not a request for help, but rather information for any one else experiencing this problem or searching for resolution.
We have been experiencing random lockups of ports ether7 and ether8 on many of our RB1200 routers in the field for several months. In some cases the port locks immediately upon linking, in other cases it takes several minutes or never occurs. The same cable plugged into a different port on the RB1200 does not exhibit this behavoir (port ether6 might suffer from this too, but I have not been able to find a test case that kills it conclusively). After a lot of traffic analysis I have identified the cause.
Any VLAN-tagged packet with a non-zero priority sent to port ether7/ether8 of a RB1200 will kill the port. The port will no longer process any inbound packets, though it will continue to link and transmit outbound packets. This applies to any kind of traffic, including ARP, ICMP, IP, neighbor broadcasts, etc. It does not matter if the corresponding VLAN is setup on the port or not. A VLAN-tagged packet with a priority of zero (the default) will function normally. Once killed, the RB1200 must be rebooted to restore the port.
In our case I finally tracked the problem source down using a VoIP phone that communicated over a VLAN prioritized its traffic and an RB1200 connected to the same network with no configuration (ARP broadcasts would kill the port). In practice any customer VLAN traffic which may be prioritized will kill the ports. This appears to be a firmware or chipset issue on the RB1200 as ports 6-8 are built into the SoC. I have submitted a support ticket to Mikrotik and am awaiting a response there.
Adrian