To my original post I would like to add that I found that this problem could be much deeper and worth looking.
I’m experiencing issues similar to this posts:
http://forum.mikrotik.com/t/10-equipment-rb435g-presenting-the-same-problem/52227/1
http://forum.mikrotik.com/t/rb435g-network-interfaces-simple-solution/53947/1
http://forum.mikrotik.com/t/problem-435g-routerboad-version-5-7-network-interfaces/50540/1
Issue is 100% reproducible for my setup: make a load to transfer data from device over Wi-Fi to wired storage and router hangs, opposite direction transfers don’t cause problem.