You might have to check the log, with logging for dhcp enabled. Or check the lease status, it probably goes till “offered” but fails to get “bound” status, when there is a repeater used.
The check to go from “offered” to “bound” never reaches the dhcp-client, so that check fails. It succeeds without the repeater.
http://forum.mikrotik.com/t/tp-link-repeater-re450-not-assigning-ip-address/118970/1
http://forum.mikrotik.com/t/ros-6-38-serious-dhcp-server-problem/105259/1
Only workaround I know is use another DHCP server, than the one on the bridge.