I have failure with my configuration involving virtual wlan. here is forum thread about the issue: http://www.dd-wrt.com/phpBB2/viewtopic.php?t=27285
Also I think ticket: #398 could be related, or the cause of both problems could be from same origin.
In short: I create new bridge that has vlan1 (WAN) and wl0.1 (Virtual WLAN) devices. Devices connecting to wl0.1 actually works as should, gets IP from ISP directly etc, but DD-WRT itself can't get an WAN IP no matter what I try. I have tried also to set wan_iface and/or wan_ifname to br1 (the name of new bridge) but no.