Thanks for replay. Is there a any solution except netinstall? I downgraded router to 6.48.5 and problem persist. I do not have any extender etc.
I think your DHCP problem is not related to the 6.49.1 or 6.48.5 release.
The issues are much older. http://forum.mikrotik.com/t/ros-6-38-serious-dhcp-server-problem/105259/1
And I believe (besides the STP disable action) that this here gets to some attempt to mitigate it (set the ff:ff:ff:ff:ff:ff broadcast MAC address) : http://forum.mikrotik.com/t/dhcp-lease-over-wireless-bridge-does-not-work-for-ethernet-clients/138721/1