We are seeing this issue on RB750GL, RB750UP and RB2011.
We have logged two tickets with Mikrotik Ticket#2012081366000093 and Ticket#2012041966000517. We were informed the issue is resolved from 5.14, but it certainly is not. We are still experiencing the issue on 5.19.
We need to get this issue resolved, and want to work with Mikrotik to do so, but responses from support@mikrotik.com are extremely slow.