Hello there!
I have a problem configuring a network as an example below:
RB 411 as accesspoint 192.168.83.4
RB 450 as router with DHCP server enabled 192.168.83.1
network is 192.168.83.0/24
I have configured an AP bridge on RB 411 with WEP authentification, 802.11b/g range and channel 8 (2447 MHz). It should be working in a way that RB 411 registers a client and then RB 450 assigns a DHCP lease to it. Everything is working great if I indicate 802.11b only as a range. But if I indicate 802.11b/g or 802.11g as a WiFi range, then the lottery begins ;-( Clients once connect directly, another time clients connect but no DHCP lease is given or clients do not register at all on AP bridge. It happens in random way, I have no idea, where the problem is ;-((( I have tried to exchange several RB411 and WiFi Atheros cards, I have tried with several laptops and it is always the same – when only 802.11b is enabled, everything is OK all the time, when 802.11b/g is enabled, then 
((( I have been trying changing data rates on RB 411 but also without success.
Any help very appreciated.