After struggling with some strange effects with Bandwidth I have learned from Mikrotik Support that Flow Control is disabled in ROS on all interface.
Why it is needed. If you have links with different speed in your network the slower links cant forward Traffic not as fast as they arrive from the faster Link. This gives not only problem when the slower link is at full speed. Problems appear at lower saturation as traffic does not travel at equal spaced intervals. So a short burst of traffic can overload the slower link.
There comes Flow control. When the buffers of the device on one side of the slower link fills up it sends pause frames in the direction of the faster link to slow down traffic. If this device is a MT Router it ignores this pause frames and sends as fast as packets arrive and overflows the slower link.
We see this happening on Licensed links where the buffers are 128KByte way before the link is filled up. Packets are dropped and overall performance drops.
MT Support does not see Flow Control as a valuable Feature and asked my to ask this mailing list if there are others who need a working Flow Control. May be then there is a developer slot to just make the knob to enable it.
Anyone else need Flow Control ?