I wrote about this years ago, sent tcpdumps, even got reply from Mikrotik’s oskarsk: http://forum.mikrotik.com/t/winbox-v3-40-released/170237/49 that they are also affected by this.
I agree that problem is probably in Wine, because it appeared with Wine update from 6 to 7, as per https://bugs.winehq.org/show_bug.cgi?id=52451 but it seems that MT is not being too active in solving this…