which SwOS version you have? in the out of box version I had lots of issues with vlans and dhcp, the switch seemed to ignore any vlan config and strip the tag on each frame received.
try to upgrade it to at least the 2.13rc5 on this thread: http://forum.mikrotik.com/t/css610-8g-2s-management-access-from-sfp-port/144001/1
EDIT: I had huge packet loss when using the latest 2.13rc12 on the SFP+ ports