Hello!
if you found a solution, please post it to me too, i have the same issue in the same time for the same router 
good luck mate, here is my post to follow, hope we got an answer, it looks the same root cause:
http://forum.mikrotik.com/t/isp-bridge-mode-cause-issue-on-rb5009/176634/1
have a great one!
Joho